# Patent

## Title
Dynamic higher-level redundancy mode management with independent silicon elements

## Abstract

A Solid-State Disk (SSD) controller enables dynamic higher-level redundancy mode management with independent silicon elements to provide graceful degradation as non-volatile (e.g. flash) memory elements fail during operation of an SSD implemented by the controller. Higher-level error correction provides correction of lower-level uncorrectable errors. If a failure of one of the non-volatile memory elements is detected, then the higher-level error correction is dynamically transitioned from operating in a current mode to operating in a new mode. The transition includes one or more of reducing free space available on the SSD, rearranging data storage of the SSD, recovering/storing failed user data (if possible), and determining/storing revised higher-level error correction information. Operation then continues in the new mode. If another failure of the non-volatile memory elements is detected, then another transition is made to another new mode.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
Priority benefit claims for this application are made in the accompanying Application Data Sheet, Request, or Transmittal (as appropriate, if any). To the extent permitted by the type of the instant application, this application incorporates by reference for all purposes the following applications, all commonly owned with the instant application at the time the invention was made:

    
    
        U.S. Provisional Application Ser. No. 61/418,846, filed Dec. 1, 2010, first named inventor Jeremy Isaac Nathaniel Werner, and entitled Dynamic Higher-Level Redundancy Mode Management with Independent Silicon Elements;
        U.S. Provisional Application Ser. No. 61/433,918, filed Jan. 18, 2011, first named inventor Jeremy Isaac Nathaniel Werner, and entitled Higher-Level Redundancy Information Computation;
        PCT Application Serial No. PCT/US11/28244, filed Mar. 11, 2011, first named inventor Hao Zhong, and entitled LDPC Erasure Decoding for Flash Memories; and
        PCT Application Serial No. PCT/US11/57914), filed Oct. 26, 2011, first named inventor Yan Li, and entitled Adaptive ECC Techniques for Flash Memory Based Data Storage.
    
    




BACKGROUND
1. Field
Advancements in flash memory storage technology are needed to provide improvements in performance, efficiency, and utility of use.
2. Related Art
Unless expressly identified as being publicly or well known, mention herein of techniques and concepts, including for context, definitions, or comparison purposes, should not be construed as an admission that such techniques and concepts are previously publicly known or otherwise part of the prior art. All references cited herein (if any), including patents, patent applications, and publications, are hereby incorporated by reference in their entireties, whether specifically incorporated or not, for all purposes.
Synopsis
The invention may be implemented in numerous ways, e.g. as a process, an article of manufacture, an apparatus, a system, a composition of matter, and a computer readable medium such as a computer readable storage medium (e.g., media in an optical and/or magnetic mass storage device such as a disk, an integrated circuit having non-volatile storage such as flash storage), or a computer network wherein program instructions are sent over optical or electronic communication links. The Detailed Description provides an exposition of one or more embodiments of the invention that enable improvements in cost, profitability, performance, efficiency, and utility of use in the field identified above. The Detailed Description includes an Introduction to facilitate understanding of the remainder of the Detailed Description. The Introduction includes Example Embodiments of one or more of systems, methods, articles of manufacture, and computer readable media in accordance with concepts described herein. As is discussed in more detail in the Conclusions, the invention encompasses all possible modifications and variations within the scope of the issued claims.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1A illustrates selected details of an embodiment of a Solid-State Disk (SSD) including an SSD controller using dynamic higher-level redundancy mode management with independent silicon elements for accessing and controlling Non-Volatile Memories (NVMs).
FIG. 1B illustrates selected details of various embodiments of systems including one or more instances of the SSD of FIG. 1A.
FIG. 2 illustrates selected details of an embodiment of mapping a Logical Page Number (LPN) portion of a Logical Block Address (LBA).
FIG. 3 illustrates selected details of an embodiment of accessing a Non-Volatile Memory (NVM) at a read unit address to produce read data organized as various read units, collectively having a length measured in quanta of read units.
FIG. 4A illustrates selected details of an embodiment of a read unit.
FIG. 4B illustrates selected details of another embodiment of a read unit.
FIG. 5 illustrates selected details of an embodiment of a header having a number of fields.
FIG. 6 illustrates selected details of an embodiment of blocks, pages, and read units of multiple NVM devices.
FIG. 7A illustrates selected details of various embodiments of higher-level redundancy techniques.
FIG. 7B illustrates selected details of an embodiment of R-blocks.
FIG. 8 illustrates selected details of an embodiment of dynamic higher-level redundancy mode management with a Redundant Array of Silicon Independent Elements (RASIE).
FIG. 9 illustrates an embodiment of read units having lower-level redundancy information of adaptive code rates protected by higher-level redundancy information stored in one or more of the read units.
FIG. 10 illustrates selected details of an embodiment of higher-level redundancy information result and data source correspondences.
FIG. 11 illustrates selected details of an embodiment of higher-level redundancy information computations.
FIG. 12 illustrates selected details of an embodiment of recovery from one (lower-level) failure (during a single operation).
FIGS. 13A-13D illustrate selected details of an embodiment of recovery from two (lower-level) failures (during a single operation).
FIGS. 14A and 14B illustrate selected details of an embodiment of computing higher-level redundancy information with respect to pages received from NVMs.
FIGS. 15A-15C illustrate selected details of an embodiment of backing out of a computation of higher-level redundancy information with respect to a write provided to NVMs.










List of Reference Symbols in Drawings








Ref. Symbol
Element Name





100
SSD Controller


101
SSD


102
Host


103
(optional) Switch/Fabric/Intermediate Controller


104
Intermediate Interfaces


105
OS


106
FirmWare (FW)


107
Driver


107D
dotted-arrow (Host Software ←→ I/O Device



Communication)


109
Application


109D
dotted-arrow (Application ←→ I/O Device



Communication via driver)


109V
dotted-arrow (Application ←→ I/O Device



Communication via VF)


110
External Interfaces


111
Host Interfaces


112C
(optional) Card Memory


113
Tag Tracking


114
Multi-Device Management Software


115
Host Software


116
I/O Card


117
I/O & Storage Devices/Resources


118
Servers


119
LAN/WAN


121
Data Processing


123
Engines


125
Control RAM


126
Scaled Data Structures


131
Buffer


133
DMA


135
ECC-X


137
Memory


141
Map


143
Table


151
Recycler


161
ECC


171
CPU


172
CPU Core


173
Command Management


175
Buffer Management


177
Translation Management


179
Coherency Management


180
Memory Interface


181
Device Management


182
Identity Management


190
Device Interfaces


191
Device Interface Logic


192
Flash Device


193
Scheduling


194
Flash Die


199
NVM


211
LBA


213
LPN


215
Logical Offset


221
Map Info for LPN


223
Read Unit Address


225
Length in Read Units


311
Read Data


313
First Read Unit


315
Last Read Unit


401A
Read Unit


401B
Read Unit


410B
Header Marker (HM)


411A
Header 1


411B
Header 1


412B
Header 2


419A
Header N


419B
Header N


421A
Data Bytes


421B
Data Bytes


422B
Data Bytes


429B
Data Bytes


431A
Optional Padding Bytes


431B
Optional Padding Bytes


501
Header


511
Type


513
Last Indicator


515
Flags


517
LPN


519
Length


521
Offset


600
Striping Direction


601, 603, 609
Devices


611, 613, 619,
Read Units


641, 643, 649,


671, 673, 679


621, 623, 629,
Pages


651, 653, 659,


681, 683, 689


631, 633, 639,
Blocks


661, 663, 669,


691, 693, 699


710.0,
Blocks


710.0B0,


710.0B1,


710.0BB


710.0P0,
Pages


710.0P1,


710.0PP


710.61,
Flash Die


710.62,


710.63


710.63B0,
Blocks


710.63B1,


710.63BB


710.63P0,
Pages


710.63P1,


710.63PP


710.64
Flash Die


710.64B0,
Blocks


710.64B1,


710.64BB


710.64P0,
Pages


710.64P1,


710.64PP


710.65
Flash Die


710.65B0,
Blocks


710.65B1,


710.65BB


710.65P0,
Pages


710.65P1,


710.65PP


720
Flash Device(s)


730
Interface Channel(s)


740
Extra Flash Device(s)


750
Extra Interface Channel(s)


760.0, 760.1,
R-blocks


760.R


801
Start


802
Operate in First Higher-Level Redundancy Mode


803
Failure?


804
Reduce Free Space


805
Rearrange Data Storage


806
Recover/Store Failed User Data


807
Determine/Store Revised Higher-Level Redundancy



Information


808
Operate in Second Higher-Level Redundancy Mode


899
End


911, 931, 951,
Read Unit


971


911.E, 931.E,
Lower-Level ECC


951.E, 971.E


911.U, 931.U,
User Data


951.U, 971.U


1001
Result


1002
Result


1003
Result


1010
R0


1011
R1


1019
Data


1401A
Start


1401B
Start


1402A
Issue Read Operation


1402B
Page Ready?


1403A
All Issued?


1403B
Perform Page-Based Computations


1404B
Pages Finished?


1499A
End


1499B
End


1501A
Start


1501B
Start


1502A
Issue Write Operation


1502B
Write OK?


1503A
All Issued?


1503B
Backout Write from Redundancy


1504B
Writes Finished?


1599A
End


1599B
End












DETAILED DESCRIPTION
A detailed description of one or more embodiments of the invention is provided below along with accompanying figures illustrating selected details of the invention. The invention is described in connection with the embodiments. The embodiments herein are understood to be merely exemplary, the invention is expressly not limited to or by any or all of the embodiments herein, and the invention encompasses numerous alternatives, modifications, and equivalents. To avoid monotony in the exposition, a variety of word labels (including but not limited to: first, last, certain, various, further, other, particular, select, some, and notable) may be applied to separate sets of embodiments; as used herein such labels are expressly not meant to convey quality, or any form of preference or prejudice, but merely to conveniently distinguish among the separate sets. The order of some operations of disclosed processes is alterable within the scope of the invention. Wherever multiple embodiments serve to describe variations in process, method, and/or program instruction features, other embodiments are contemplated that in accordance with a predetermined or a dynamically determined criterion perform static and/or dynamic selection of one of a plurality of modes of operation corresponding respectively to a plurality of the multiple embodiments. Numerous specific details are set forth in the following description to provide a thorough understanding of the invention. The details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of the details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
Introduction
This introduction is included only to facilitate the more rapid understanding of the Detailed Description; the invention is not limited to the concepts presented in the introduction (including explicit examples, if any), as the paragraphs of any introduction are necessarily an abridged view of the entire subject and are not meant to be an exhaustive or restrictive description. For example, the introduction that follows provides overview information limited by space and organization to only certain embodiments. There are many other embodiments, including those to which claims will ultimately be drawn, discussed throughout the balance of the specification.
Acronyms
At least some of the various shorthand abbreviations (e.g. acronyms) defined here refer to certain elements used herein.











Acronym
Description







AHCI
Advanced Host Controller Interface


API
Application Program Interface


ATA
Advanced Technology Attachment (AT Attachment)


BCH
Bose Chaudhuri Hocquenghem


CD
Compact Disk


CF
Compact Flash


CMOS
Complementary Metal Oxide Semiconductor


CPU
Central Processing Unit


CRC
Cyclic Redundancy Check


DAS
Direct Attached Storage


DDR
Double-Data-Rate


DMA
Direct Memory Access


DNA
Direct NAND Access


DRAM
Dynamic Random Access Memory


DVD
Digital Versatile/Video Disk


DVR
Digital Video Recorder


ECC
Error-Correcting Code


eMMC
Embedded MultiMediaCard


eSATA
external Serial Advanced Technology Attachment


GPS
Global Positioning System


HDD
Hard Disk Drive


I/O
Input/Output


IC
Integrated Circuit


IDE
Integrated Drive Electronics


JPEG
Joint Photographic Experts Group


LAN
Local Area Network


LBA
Logical Block Address


LDPC
Low-Density Parity-Check


LPN
Logical Page Number


MLC
Multi-Level Cell


MMC
MultiMediaCard


MPEG
Moving Picture Experts Group


NAS
Network Attached Storage


NCQ
Native Command Queuing


NVM
Non-Volatile Memory


ONA
Optimized NAND Access


ONFI
Open NAND Flash Interface


OS
Operating System


PC
Personal Computer


PCIe
Peripheral Component Interconnect express (PCI express)


PDA
Personal Digital Assistant


PHY
PHYsical interface


POS
Point Of Sale


RAID
Redundant Array of Inexpensive/Independent Disks


RASIE
Redundant Array of Silicon Independent Elements


RS
Reed-Solomon


SAN
Storage Attached Network


SAS
Serial Attached Small Computer System Interface (Serial



SCSI)


SATA
Serial Advanced Technology Attachment (Serial ATA)


SCSI
Small Computer System Interface


SD
Secure Digital


SDR
Single-Data-Rate


SLC
Single-Level Cell


SMART
Self-Monitoring Analysis and Reporting Technology


SRAM
Static Random Access Memory


SSD
Solid-State Disk/Drive


UFS
Unified Flash Storage


USB
Universal Serial Bus


VF
Virtual Function


WAN
Wide Area Network









NAND flash memory uses an array of floating gate transistors to store information. In SLC technology, each bit cell (e.g. floating gate transistor) is enabled to store one bit of information. In MLC technology, each bit cell is enabled to store multiple bits of information. As manufacturing technology (e.g. CMOS technology) scales down, each floating gate stores fewer electrons. Further, as storage capacity and density increase, each bit cell stores more bits. Therefore, values stored in the bit cells are represented by smaller voltage ranges. Uncertainties in sensing and/or changes in amount of stored electrons over time increase a probability for data to be stored or read incorrectly. Use of one or more redundancy and/or ECC techniques (e.g. at a lower-level) enables correct retrieval of otherwise corrupted data from NAND flash memory, overcoming, in some usage scenarios, some of the aforementioned difficulties.
Some types of SSDs use flash memory to provide non-volatile storage (e.g., the flash memory retains information without application of power). Use of one or more ECC and/or redundancy techniques (e.g. at a higher-level) enables correct retrieval of otherwise corrupted data from flash memory, and/or enables proper system-level operation of an SSD even when one or more flash memory elements fail intermittently or permanently.
For example, an SSD controller enables dynamic higher-level redundancy mode management with independent silicon elements to provide graceful degradation as one or more NVM (e.g. flash) elements fail during operation of an SSD implemented in part by the controller. A portion of the NVM is read. If an error occurs that is not correctable using lower-level redundancy and/or error correction (such as in accordance with one or more ECC techniques), then higher-level error correction (such as in accordance with one or more RASIE techniques and/or dynamic higher-level redundancy mode management techniques) is used to attempt to correct the error. If a failure of one of the NVM elements is detected by the lower-level and/or the higher-level error correction, and/or by other techniques (such as a failing status reported by one or more of the NVM elements), then the higher-level error correction is dynamically transitioned from operating in a current mode to operating in a new mode. The transition includes one or more of reducing free space available on the SSD, rearranging data storage of the SSD, recovering/storing failed user data (if possible), and determining/storing revised higher-level error correction information. Operation then continues in the new mode. If another failure of another one of the NVM elements is detected with the higher-level error correction now operating in the new mode, then another transition is made to another higher-level error correction mode. Writing the NVM is in accordance with a higher-level error correction operating mode, including determining/storing higher-level error correction information in accordance with the higher-level error correction operating mode and write data.
Determining/storing higher-level error correction information is in accordance, in some embodiments and/or usage scenarios, with computation of higher-level redundancy information. Higher-level redundancy information computation enables an SSD controller to provide higher-level redundancy capabilities to maintain reliable operation in a context of failures of non-volatile (e.g. flash) memory elements during operation of an SSD implemented in part by the controller. A first portion of higher-level redundancy information is computed using parity coding via an XOR of all pages in a portion of data (e.g. a stripe) to be protected by the higher-level redundancy information. A second portion of the higher-level redundancy information is computed using a weighted-sum technique, each page in the portion being assigned a unique non-zero “index” as a weight when computing the weighted-sum. Arithmetic is performed over a finite field (such as a Galois Field, or such as the integers mod p where p is a prime).
The portions of the higher-level redundancy information are computable in any order, such as an order determined by an order of completion of one or more read operations performed on NVM elements, or such as an order based on order of data returned and/or available from NVM elements, enabling, in various embodiments, reduced or eliminated buffering. The any order computability enables, in various embodiments, computing recovery data values and/or backing out of a write using relatively little temporary and/or intermediate buffering and/or state. The portions of the higher-level redundancy information are computable with any degree of parallelism, such as determined by available dedicated hardware elements, enabling, in various embodiments, reduced latency processing and/or reduced memory (e.g. NVM) bandwidth usage.
In some embodiments, an I/O device, such as an SSD, includes an SSD controller. The SSD controller acts as a bridge between the host interface and NVM of the SSD, and executes commands of a host protocol sent from a computing host via a host interface of the SSD. At least some of the commands direct the SSD to write and read the NVM with data sent from and to the computing host, respectively. In further embodiments, the SSD controller is enabled to use a map to translate between LBAs of the host protocol and physical storage addresses in the NVM. In further embodiments, at least a portion of the map is used for private storage (not visible to the computing host) of the I/O device. For example, a portion of the LBAs not accessible by the computing host is used by the I/O device to manage access to logs, statistics, or other private data.
In some embodiments, accessing compressed data of varying-sized quanta in NVM provides improved storage efficiency in some usage scenarios. For example, an SSD controller receives (uncompressed) data from a computing host (e.g., relating to a disk write command), compresses the data, and stores the compressed data into flash memory. In response to a subsequent request from the computing host (e.g., relating to a disk read command), the SSD controller reads the compressed data from the flash memory, uncompresses the compressed data, and provides the uncompressed data to the computing host. The compressed data is stored in the flash memory according to varying-sized quanta, the quanta size varying due to, e.g., compression algorithm, operating mode, and compression effectiveness on various data. The SSD controller uncompresses the data in part by consulting an included map table to determine where header(s) are stored in the flash memory. The SSD controller parses the header(s) obtained from the flash memory to determine where appropriate (compressed) data is stored in the flash memory. The SSD controller uncompresses the appropriate data from the flash memory to produce the uncompressed data to provide to the computing host. In the instant application, uncompress (and variants thereof) is synonymous with decompress (and variants thereof).
In various embodiments, an SSD controller includes a host interface for interfacing with a computing host, an interface for interfacing with NVM such as flash memory, and circuitry for controlling the interfaces and performing (and/or controlling various aspects of the performing) compressing and uncompressing, as well as lower-level error correction, higher-level error correction, and dynamic higher-level redundancy mode management with independent silicon elements.
According to various embodiments, some host interfaces are compatible with one or more of a USB interface standard, a CF interface standard, an MMC interface standard, an eMMC interface standard, a Thunderbolt interface standard, a UFS interface standard, an SD interface standard, a Memory Stick interface standard, an xD-picture card interface standard, an IDE interface standard, a SATA interface standard, a SCSI interface standard, a SAS interface standard, and a PCIe interface standard. According to various embodiments, the computing host is all or any portions of a computer, a workstation computer, a server computer, a storage server, a SAN, a NAS device, a DAS device, a storage appliance, a PC, a laptop computer, a notebook computer, a netbook computer, a tablet device or computer, an ultrabook computer, an electronic reading device (such as an e-reader), a PDA, a navigation system, a (handheld) GPS device, an automotive control system, an automotive media control system or computer, a printer, copier or fax machine or all-in-one device, a POS device, a cash-register, a media player, a television, a media recorder, a DVR, a digital camera, a cellular handset, a cordless telephone handset, and an electronic game. In some embodiments, an interfacing host (such as an SAS/SATA bridge) operates as a computing host and/or as a bridge to a computing host.
In various embodiments, the SSD controller includes one or more processors. The processors execute firmware to control and/or perform operation of the SSD controller. The SSD controller communicates with the computing host to send and receive commands and/or status as well as data. The computing host executes one or more of an operating system, a driver, and an application. Communication by the computing host with the SSD controller is optionally and/or selectively via the driver and/or via the application. In a first example, all communication to the SSD controller is via the driver, and the application provides higher-level commands to the driver that the driver translates into specific commands for the SSD controller. In a second example, the driver implements a bypass mode and the application is enabled to send specific commands to the SSD controller via the driver. In a third example, a PCIe SSD controller supports one or more Virtual Functions (VFs), enabling an application, once configured, to communicate directly with the SSD controller, bypassing the driver.
According to various embodiments, some SSDs are compatible with form-factors, electrical interfaces, and/or protocols used by magnetic and/or optical non-volatile storage, such as HDDs, CD drives, and DVD drives. In various embodiments, SSDs use various combinations of zero or more parity codes, zero or more RS codes, zero or more BCH codes, zero or more Viterbi or other trellis codes, and zero or more LDPC codes.
Example Embodiments
In concluding the introduction to the detailed description, what follows is a collection of example embodiments, including at least some explicitly enumerated as “ECs” (Example Combinations), providing additional description of a variety of embodiment types in accordance with the concepts described herein; these examples are not meant to be mutually exclusive, exhaustive, or restrictive; and the invention is not limited to these example embodiments but rather encompasses all possible modifications and variations within the scope of the issued claims.
EC1) A system comprising:

    
    
        means for computing k redundant data portions to protect n-k useful data portions;
        means for storing each of the k redundant data portions and each of the n-k useful data portions in separate corresponding areas, each of the corresponding areas in a respective one of n physical devices;
        means for, subsequent to a failure such that one of the corresponding areas is no longer usable, computing j redundant data portions to protect n-1-j useful data portions; and
        wherein j<=k.
    
    


EC2) The system of EC1, wherein the means for computing k redundant data portions to protect n-k useful data portions is operable in a first data protection mode, the means for computing j redundant data portions to protect n-1-j useful data portions is operable in a second data protection mode, and further comprising means for, in response to the failure, switching from operating in the first data protection mode to operating in the second data protection mode.
EC3) The system of EC1, wherein when j==k, a total amount of the useful data portions is decreased and a degree of protection is at least preserved.
EC4) The system of EC3, wherein the degree of protection is protection against failures of up to j of the corresponding areas.
EC5) The system of EC1, wherein when j==k-1 and j>=1, a total amount of the useful data portions is preserved, a degree of protection is decreased, and the useful data portions are protected.
EC6) The system of EC5, wherein the decreased degree of protection is protection against failures of up to j-1 of the corresponding areas.
EC7) The system of EC1,

    
    
        wherein each of the n physical devices comprises a plurality of the corresponding areas;
        further comprising means for storing, in each of a plurality of sets of the corresponding areas, a respective set of data comprising a useful data subset and a redundant data subset protecting the useful data subset, the redundant data subset stored in distinct ones of the n physical devices from the useful data subset; and
        wherein each of the sets of the corresponding areas comprises no more than one corresponding area of each one of the n physical devices, and the means for storing is in accordance with each of the respective sets of data optionally being stored in a different set of n or less of the n physical devices.
    
    


EC8) The system of EC7, wherein prior to the failure, the useful data subset of a particular one of the sets of data comprises the n-k useful data portions, and the redundant data subset of the particular set of data comprises the k redundant data portions.
EC9) The system of EC7, wherein the means for storing is in accordance with a first one of the corresponding areas in a particular one of the n physical devices being used to store a portion of the useful data subset of a first one of the sets of data, and is further in accordance with a second one of the corresponding areas in the particular physical device being used to store a portion or all of the redundant data subset of a second one of the sets of data.
EC10) The system of EC7, wherein an amount of storage in a first one of the corresponding areas differs from an amount of storage in a second one of the corresponding areas.
EC11) The system of EC10, wherein the first corresponding area and the second corresponding area are in a same one of the n physical devices.
EC12) A system comprising:

    
    
        means for operating in a first higher-level redundancy mode comprising means for storing n information portions in n respective non-overlapping areas of memory;
        means for operating in a second higher-level redundancy mode comprising means for storing n-1 information portions in n-1 respective non-overlapping areas of the memory;
        means for detecting a failure of a failing one of the n respective non-overlapping areas;
        means for, in response to the failure, dynamically transitioning from operating via the means for operating in the first higher-level redundancy mode to operating via the means for operating in the second higher-level redundancy mode, the n-1 of the n respective non-overlapping areas being the n respective non-overlapping areas excluding the failing one of the n respective non-overlapping areas;
        wherein each of the n information portions comprises respective n-k data information portions and respective k redundant information portions computed to protect the respective n-k data information portions;
        wherein each of the n-1 information portions comprises respective n-1-j data information portions and respective j redundant information portions computed to protect the respective n-1-j data information portions;
        wherein j<=k; and
        wherein each of the n respective non-overlapping areas is in a respective one of n physical devices of the memory.
    
    


EC13) The system of EC12, wherein when j==k, a total amount of the data information portions is decreased and a degree of protection is at least preserved.
EC14) The system of EC13, wherein the degree of protection is protection against failures of up to j of the n respective non-overlapping areas.
EC15) The system of EC12, wherein when j==k-1 and j>=1, a total amount of the data information portions is preserved, a degree of protection is decreased, and the data information portions are protected.
EC16) The system of EC15, wherein the decreased degree of protection is protection against failures of up to j-1 of the n respective non-overlapping areas.
EC17) The system of EC1 or EC12, wherein at least one of the means for storing is responsive to write requests from a computing host.
EC18) The system of EC1 or EC12, wherein at least one of the means for storing comprises means for operating a flash memory interface.
EC19) The system of EC1 or EC12, wherein at least one of the n physical devices comprises one or more flash memories.
EC20) A system comprising:

    
    
        means for managing one or more flash memories in accordance with a current higher-level redundancy mode in response to read and/or write requests from a computing host; and
        means for dynamically transitioning the current higher-level redundancy mode in response to detecting a failure of one or more portions of one or more of the flash memories.
    
    


EC21) The system of EC20, wherein the means for dynamically transitioning comprises means for reducing free space.
EC22) The system of EC20, wherein the means for dynamically transitioning comprises means for rearranging data storage in accordance with a target higher-level redundancy mode.
EC23) The system of EC20, wherein the means for dynamically transitioning comprises means for determining and storing revised higher-level redundancy information in accordance with a target higher-level redundancy mode.
EC24) The system of EC20, wherein the current higher-level redundancy mode is a first higher-level redundancy mode and the means for dynamically transitioning the current higher-level redundancy mode comprises means for transitioning the current higher-level redundancy mode to a second higher-level redundancy mode in response to a first failure and means for transitioning the current higher-level redundancy mode to a third higher-level redundancy mode in response to a second failure.
EC25) The system of EC24, wherein the second failure is subsequent to the first failure and less free space is available in the third higher-level redundancy mode than in the second higher-level redundancy mode.
EC26) The system of EC17 or EC20, further comprising means for interfacing the requests with the computing host.
EC27) The system of EC26, wherein the means for interfacing the requests with the computing host is compatible with a storage interface standard.
EC28) The system of EC20, further comprising means for interfacing the means for managing with the flash memories.
EC29) The system of EC28, wherein the means for interfacing the means for managing with the flash memories comprises means for operating a flash memory interface.
EC30) The system of EC20, further comprising:

    
    
        means for interfacing the requests with the computing host; and
        means for interfacing the managing with the flash memories.
    
    


EC31) The system of EC27, wherein the system is implemented in a single Integrated Circuit (IC).
EC32) The system of EC27, wherein the system is implemented in a Solid-State Disk (SSD).
EC33) The system of EC17 or EC20, further comprising means for operating the computing host to generate at least some of the read and/or write requests.
EC34) The system of EC19 or EC20, further comprising means for operating at least one of the flash memories.
EC35) A method comprising:

    
    
        computing k redundant data portions to protect n-k useful data portions;
        storing each of the k redundant data portions and each of the n-k useful data portions in separate corresponding areas, each of the corresponding areas in a respective one of n physical devices;
        subsequent to a failure such that one of the corresponding areas is no longer usable, computing j redundant data portions to protect n-1-j useful data portions; and
        wherein j<=k.
    
    


EC36) The method of EC35, wherein the computing k redundant data portions to protect n-k useful data portions is a first data protection mode, the computing j redundant data portions to protect n-1-j useful data portions is a second data protection mode, and further comprising in response to the failure, switching from the first data protection mode to the second data protection mode.
EC37) The method of EC35, wherein when j==k, a total amount of the useful data portions is decreased and a degree of protection is at least preserved.
EC38) The method of EC37, wherein the degree of protection is protection against failures of up to j of the corresponding areas.
EC39) The method of EC35, wherein when j==k-1 and j>=1, a total amount of the useful data portions is preserved, a degree of protection is decreased, and the useful data portions are protected.
EC40) The method of EC39, wherein the decreased degree of protection is protection against failures of up to j-1 of the corresponding areas.
EC41) The method of EC35,

    
    
        wherein each of the n physical devices comprises a plurality of the corresponding areas;
        further comprising storing, in each of a plurality of sets of the corresponding areas, a respective set of data comprising a useful data subset and a redundant data subset protecting the useful data subset, the redundant data subset stored in distinct ones of the n physical devices from the useful data subset; and
        wherein each of the sets of the corresponding areas comprises no more than one corresponding area of each one of the n physical devices, and the storing is in accordance with each of the respective sets of data optionally being stored in a different set of n or less of the n physical devices.
    
    


EC42) The method of EC41, wherein prior to the failure, the useful data subset of a particular one of the sets of data comprises the n-k useful data portions, and the redundant data subset of the particular set of data comprises the k redundant data portions.
EC43) The method of EC41, wherein the storing is in accordance with a first one of the corresponding areas in a particular one of the n physical devices being used to store a portion of the useful data subset of a first one of the sets of data, and is further in accordance with a second one of the corresponding areas in the particular physical device being used to store a portion or all of the redundant data subset of a second one of the sets of data.
EC44) The method of EC41, wherein an amount of storage in a first one of the corresponding areas differs from an amount of storage in a second one of the corresponding areas.
EC45) The method of EC44, wherein the first corresponding area and the second corresponding area are in a same one of the n physical devices.
EC46) A method comprising:

    
    
        operating in a first higher-level redundancy mode comprising storing n information portions in n respective non-overlapping areas of memory;
        detecting a failure of a failing one of the n respective non-overlapping areas;
        in response to the failure, dynamically transitioning from operating in the first higher-level redundancy mode to operating in a second higher-level redundancy mode comprising storing n-1 information portions in n-1 of the n respective non-overlapping areas, the n-1 of the n respective non-overlapping areas being the n respective non-overlapping areas excluding the failing one of the n respective non-overlapping areas;
        wherein each of the n information portions comprises respective n-k data information portions and respective k redundant information portions computed to protect the respective n-k data information portions;
        wherein each of the n-1 information portions comprises respective n-1-j data information portions and respective j redundant information portions computed to protect the respective n-1-j data information portions;
        wherein j<=k; and
        wherein each of the n respective non-overlapping areas is in a respective one of n physical devices of the memory.
    
    


EC47) The method of EC46, wherein when j==k, a total amount of the data information portions is decreased and a degree of protection is at least preserved.
EC48) The method of EC47, wherein the degree of protection is protection against failures of up to j of the n respective non-overlapping areas.
EC49) The method of EC46, wherein when j==k-1 and j>=1, a total amount of the data information portions is preserved, a degree of protection is decreased, and the data information portions are protected.
EC50) The method of EC49, wherein the decreased degree of protection is protection against failures of up to j-1 of the n respective non-overlapping areas.
EC51) The method of EC35 or EC46, wherein at least a portion of at least one of the acts of storing is in response to write requests from a computing host.
EC52) The method of EC35 or EC46, wherein at least one of the acts of storing comprises operating a flash memory interface.
EC53) The method of EC35 or EC46, wherein at least one of the n physical devices comprises one or more flash memories.
EC54) A method comprising:

    
    
        managing one or more flash memories in accordance with a current higher-level redundancy mode in response to read and/or write requests from a computing host; and
        dynamically transitioning the current higher-level redundancy mode in response to detecting a failure of one or more portions of one or more of the flash memories.
    
    


EC55) The method of EC54, wherein the dynamically transitioning comprises reducing free space.
EC56) The method of EC54, wherein the dynamically transitioning comprises rearranging data storage in accordance with a target higher-level redundancy mode.
EC57) The method of EC54, wherein the dynamically transitioning comprises determining and storing revised higher-level redundancy information in accordance with a target higher-level redundancy mode.
EC58) The method of EC54, wherein the current higher-level redundancy mode is a first higher-level redundancy mode and the dynamically transitioning the current higher-level redundancy mode transitions the current higher-level redundancy mode to a second higher-level redundancy mode in response to a first failure and transitions the current higher-level redundancy mode to a third higher-level redundancy mode in response to a second failure.
EC59) The method of EC58, wherein the second failure is subsequent to the first failure and less free space is available in the third higher-level redundancy mode than in the second higher-level redundancy mode.
EC60) The method of EC51 or EC54, further comprising interfacing the requests with the computing host.
EC61) The method of EC60, wherein the interfacing the requests with the computing host is compatible with a storage interface standard.
EC62) The method of EC54, further comprising interfacing the managing with the flash memories.
EC63) The method of EC62, wherein the interfacing the managing with the flash memories comprises operating a flash memory interface.
EC64) The method of EC54, further comprising:

    
    
        interfacing the requests with the computing host; and
        interfacing the managing with the flash memories.
    
    


EC65) The method of EC61, wherein the method is implemented in a single Integrated Circuit (IC).
EC66) The method of EC61, wherein the method is implemented in a Solid-State Disk (SSD).
EC67) The method of EC51 or EC54, further comprising operating the computing host to generate at least some of the read and/or write requests.
EC68) The method of EC53 or EC54, further comprising operating at least one of the flash memories.
EC69) A system comprising:

    
    
        a host interface enabled to interface to a computing host;
        a memory interface enabled to interface to at least n physical devices;
        a controller enabled to
        
            compute k redundant data portions to protect n-k useful data portions,
            in response to one or more write commands received from the computing host via the host interface, store each of the k redundant data portions and each of the n-k useful data portions in separate corresponding areas, each of the corresponding areas in a respective one of the n physical devices, and
            subsequent to a failure such that one of the corresponding areas is no longer usable, compute j redundant data portions to protect n-1-j useful data portions; and
        
        
        wherein j<=k.
    
    


EC70) The system of EC69, further comprising a hardware logic circuit enabled to compute all or any portions of any one or more of the k redundant data portions.
EC71) The system of EC69, wherein the computing k redundant data portions to protect n-k useful data portions is in accordance with the controller operating in a first data protection mode, the computing j redundant data portions to protect n-1-j useful data portions is in accordance with the controller operating in a second data protection mode, and the controller is further enabled, in response to the failure, to switch from operating in the first data protection mode to operating in the second data protection mode.
EC72) The system of EC69, wherein when j==k, a total amount of the useful data portions is decreased and a degree of protection is at least preserved.
EC73) The system of EC72, wherein the degree of protection is protection against failures of up to j of the corresponding areas.
EC74) The system of EC69, wherein when j==k-1 and j>=1, a total amount of the useful data portions is preserved, a degree of protection is decreased, and the useful data portions are protected.
EC75) The system of EC74, wherein the decreased degree of protection is protection against failures of up to j-1 of the corresponding areas.
EC76) The system of EC69,

    
    
        wherein each of the n physical devices comprises a plurality of the corresponding areas;
        wherein the controller is further enabled to store, in each of a plurality of sets of the corresponding areas, a respective set of data comprising a useful data subset and a redundant data subset protecting the useful data subset, the redundant data subset stored in distinct ones of the n physical devices from the useful data subset; and
        wherein each of the sets of the corresponding areas comprises no more than one corresponding area of each one of the n physical devices, and the storing is in accordance with each of the respective sets of data optionally being stored in a different set of n or less of the n physical devices.
    
    


EC77) The system of EC76, wherein prior to the failure, the useful data subset of a particular one of the sets of data comprises the n-k useful data portions, and the redundant data subset of the particular set of data comprises the k redundant data portions.
EC78) The system of EC76, wherein the storing is in accordance with a first one of the corresponding areas in a particular one of the n physical devices being used to store a portion of the useful data subset of a first one of the sets of data, and is further in accordance with a second one of the corresponding areas in the particular physical device being used to store a portion or all of the redundant data subset of a second one of the sets of data.
EC79) The system of EC76, wherein an amount of storage in a first one of the corresponding areas differs from an amount of storage in a second one of the corresponding areas.
EC80) The system of EC79, wherein the first corresponding area and the second corresponding area are in a same one of the n physical devices.
EC81) A system comprising:

    
    
        a host interface enabled to interface to a computing host;
        a memory interface enabled to interface to at least n physical devices;
        a controller enabled to
        
            operate in a first higher-level redundancy mode in accordance with storing n information portions in n respective non-overlapping areas of memory;
            detect a failure of a failing one of the n respective non-overlapping areas;
            in response to the failure, dynamically transitioning from operating in the first higher-level redundancy mode to operating in a second higher-level redundancy mode, the second higher-level redundancy mode being in accordance with storing n-1 information portions in n-1 of the n respective non-overlapping areas, the n-1 of the n respective non-overlapping areas being the n respective non-overlapping areas excluding the failing one of the n respective non-overlapping areas;
            wherein each of the n information portions comprises respective n-k data information portions and respective k redundant information portions computed to protect the respective n-k data information portions;
            wherein each of the n-1 information portions comprises respective n-1-j data information portions and respective j redundant information portions computed to protect the respective n-1-j data information portions;
        
        
        wherein j<=k; and
        wherein each of the n respective non-overlapping areas is in a respective one of n physical devices of the memory.
    
    


EC82) The system of EC81, further comprising a hardware logic circuit enabled to compute all or any portions of any one or more of the k redundant information portions.
EC83) The system of EC81, wherein when j==k, a total amount of the data information portions is decreased and a degree of protection is at least preserved.
EC84) The system of EC83, wherein the degree of protection is protection against failures of up to j of the n respective non-overlapping areas.
EC85) The system of EC81, wherein when j==k-1 and j>=1, a total amount of the data information portions is preserved, a degree of protection is decreased, and the data information portions are protected.
EC86) The system of EC85, wherein the decreased degree of protection is protection against failures of up to j-1 of the n respective non-overlapping areas.
EC87) The system of EC69 or EC81, wherein at least a portion of at least one of the acts of storing is in response to write requests from the computing host.
EC88) The system of EC69 or EC81, wherein the memory interface comprises a flash memory interface.
EC89) The system of EC69 or EC81, wherein at least one of the n physical devices comprises one or more flash memories.
EC90) A system comprising:

    
    
        a host interface enabled to interface to a computing host;
        a controller enabled to
        
            manage one or more flash memories in accordance with a current higher-level redundancy mode in response to read and/or write requests from the computing host; and
            dynamically transition the current higher-level redundancy mode in response to detecting a failure of one or more portions of one or more of the flash memories.
        
        
    
    


EC91) The system of EC90, further comprising a hardware logic circuit enabled to compute redundancy information usable in the current higher-level redundancy mode.
EC92) The system of EC90, wherein the controller is further enabled to reduce free space in accordance with the dynamic transition.
EC93) The system of EC90, wherein the controller is further enabled to rearrange data storage in accordance with a target higher-level redundancy mode and in accordance with the dynamic transition.
EC94) The system of EC90, wherein the controller is further enabled to determine and store revised higher-level redundancy information in accordance with a target higher-level redundancy mode and in accordance with the dynamic transition
EC95) The system of EC90, wherein the current higher-level redundancy mode is a first higher-level redundancy mode and the controller is further enabled to transition the current higher-level redundancy mode to a second higher-level redundancy mode in response to a first failure and to transition the current higher-level redundancy mode to a third higher-level redundancy mode in response to a second failure.
EC96) The system of EC95, wherein the second failure is subsequent to the first failure and less free space is available in the third higher-level redundancy mode than in the second higher-level redundancy mode.
EC97) The system of EC90, wherein the host interface is compatible with a storage interface standard.
EC98) The system of EC90, further comprising a flash memory interface enabled to interface with the flash memories.
EC99) The system of EC88 or EC97, wherein the system is implemented in a single Integrated Circuit (IC).
EC100) The system of EC88 or EC97, wherein the system is implemented in a Solid-State Disk (SSD).
EC101) The system of EC87 or EC90, further comprising the computing host.
EC102) The system of EC89 or EC90, further comprising at least one of the flash memories.
EC103) A tangible computer readable medium having a set of instructions stored therein that when executed by a processing element cause the processing element to perform operations comprising:

    
    
        computing k redundant data portions to protect n-k useful data portions;
        storing each of the k redundant data portions and each of the n-k useful data portions in separate corresponding areas, each of the corresponding areas in a respective one of n physical devices;
        subsequent to a failure such that one of the corresponding areas is no longer usable, computing j redundant data portions to protect n-1-j useful data portions; and
        wherein j<=k.
    
    


EC104) The tangible computer readable medium of EC103, wherein the computing k redundant data portions to protect n-k useful data portions is in accordance with a first data protection mode, the computing j redundant data portions to protect n-1-j useful data portions is in accordance with a second data protection mode, and further comprising in response to the failure, switching from the first data protection mode to the second data protection mode.
EC105) The tangible computer readable medium of EC103, wherein when j==k, a total amount of the useful data portions is decreased and a degree of protection is at least preserved.
EC106) The tangible computer readable medium of EC105, wherein the degree of protection is protection against failures of up to j of the corresponding areas.
EC107) The tangible computer readable medium of EC103, wherein when j==k-1 and j>=1, a total amount of the useful data portions is preserved, a degree of protection is decreased, and the useful data portions are protected.
EC108) The tangible computer readable medium of EC107, wherein the decreased degree of protection is protection against failures of up to j-1 of the corresponding areas.
EC109) The tangible computer readable medium of EC103,

    
    
        wherein each of the n physical devices comprises a plurality of the corresponding areas;
        further comprising storing, in each of a plurality of sets of the corresponding areas, a respective set of data comprising a useful data subset and a redundant data subset protecting the useful data subset, the redundant data subset stored in distinct ones of the n physical devices from the useful data subset; and
        wherein each of the sets of the corresponding areas comprises no more than one corresponding area of each one of the n physical devices, and the storing is in accordance with each of the respective sets of data optionally being stored in a different set of n or less of the n physical devices.
    
    


EC110) The tangible computer readable medium of EC109, wherein prior to the failure, the useful data subset of a particular one of the sets of data comprises the n-k useful data portions, and the redundant data subset of the particular set of data comprises the k redundant data portions.
EC111) The tangible computer readable medium of EC109, wherein the storing is in accordance with a first one of the corresponding areas in a particular one of the n physical devices being used to store a portion of the useful data subset of a first one of the sets of data, and is further in accordance with a second one of the corresponding areas in the particular physical device being used to store a portion or all of the redundant data subset of a second one of the sets of data.
EC112) The tangible computer readable medium of EC109, wherein an amount of storage in a first one of the corresponding areas differs from an amount of storage in a second one of the corresponding areas.
EC113) The tangible computer readable medium of EC112, wherein the first corresponding area and the second corresponding area are in a same one of the n physical devices.
EC114) A tangible computer readable medium having a set of instructions stored therein that when executed by a processing element cause the processing element to perform operations comprising:

    
    
        operating in a first higher-level redundancy mode comprising storing n information portions in n respective non-overlapping areas of memory;
        detecting a failure of a failing one of the n respective non-overlapping areas;
        in response to the failure, dynamically transitioning from operating in the first higher-level redundancy mode to operating in a second higher-level redundancy mode comprising storing n-1 information portions in n-1 of the n respective non-overlapping areas, the n-1 of the n respective non-overlapping areas being the n respective non-overlapping areas excluding the failing one of the n respective non-overlapping areas;
        wherein each of the n information portions comprises respective n-k data information portions and respective k redundant information portions computed to protect the respective n-k data information portions;
        wherein each of the n-1 information portions comprises respective n-1-j data information portions and respective j redundant information portions computed to protect the respective n-1-j data information portions;
        wherein j<=k; and
        wherein each of the n respective non-overlapping areas is in a respective one of n physical devices of the memory.
    
    


EC115) The tangible computer readable medium of EC114, wherein when j==k, a total amount of the data information portions is decreased and a degree of protection is at least preserved.
EC116) The tangible computer readable medium of EC115, wherein the degree of protection is protection against failures of up to j of the n respective non-overlapping areas.
EC117) The tangible computer readable medium of EC114, wherein when j==k-1 and j>=1, a total amount of the data information portions is preserved, a degree of protection is decreased, and the data information portions are protected.
EC118) The tangible computer readable medium of EC117, wherein the decreased degree of protection is protection against failures of up to j-1 of the n respective non-overlapping areas.
EC119) The tangible computer readable medium of EC103 or EC114, wherein at least a portion of at least one of the acts of storing is in response to write requests from a computing host.
EC120) The tangible computer readable medium of EC103 or EC114, wherein at least one of the acts of storing comprises operating a flash memory interface.
EC121) The tangible computer readable medium of EC103 or EC114, wherein at least one of the n physical devices comprises one or more flash memories.
EC122) A tangible computer readable medium having a set of instructions stored therein that when executed by a processing element cause the processing element to perform operations comprising:

    
    
        managing one or more flash memories in accordance with a current higher-level redundancy mode in response to read and/or write requests from a computing host; and
        dynamically transitioning the current higher-level redundancy mode in response to detecting a failure of one or more portions of one or more of the flash memories.
    
    


EC123) The tangible computer readable medium of EC122, wherein the dynamically transitioning comprises reducing free space.
EC124) The tangible computer readable medium of EC122, wherein the dynamically transitioning comprises rearranging data storage in accordance with a target higher-level redundancy mode.
EC125) The tangible computer readable medium of EC122, wherein the dynamically transitioning comprises determining and storing revised higher-level redundancy information in accordance with a target higher-level redundancy mode.
EC126) The tangible computer readable medium of EC122, wherein the current higher-level redundancy mode is a first higher-level redundancy mode and the dynamically transitioning the current higher-level redundancy mode transitions the current higher-level redundancy mode to a second higher-level redundancy mode in response to a first failure and transitions the current higher-level redundancy mode to a third higher-level redundancy mode in response to a second failure.
EC127) The tangible computer readable medium of EC126, wherein the second failure is subsequent to the first failure and less free space is available in the third higher-level redundancy mode than in the second higher-level redundancy mode.
EC128) The tangible computer readable medium of EC119 or EC122, further comprising interfacing the requests with the computing host.
EC129) The tangible computer readable medium of EC128, wherein the interfacing the requests with the computing host is compatible with a storage interface standard.
EC130) The tangible computer readable medium of EC122, further comprising interfacing the managing with the flash memories.
EC131) The tangible computer readable medium of EC130, wherein the interfacing the managing with the flash memories comprises operating a flash memory interface.
EC132) The tangible computer readable medium of EC122, further comprising:

    
    
        interfacing the requests with the computing host; and
        interfacing the managing with the flash memories.
    
    


EC133) The tangible computer readable medium of EC129, wherein the tangible computer readable medium is implemented in a single Integrated Circuit (IC).
EC134) The tangible computer readable medium of EC129, wherein the tangible computer readable medium is implemented in a Solid-State Disk (SSD).
EC135) The tangible computer readable medium of EC119 or EC122, further comprising operating the computing host to generate at least some of the read and/or write requests.
EC136) The tangible computer readable medium of EC121 or EC122, further comprising operating at least one of the flash memories.
EC137) Any of the foregoing ECs having a storage interface standard, wherein the storage interface standard comprises one or more of

    
    
        a Universal Serial Bus (USB) interface standard,
        a Compact Flash (CF) interface standard,
        a MultiMediaCard (MMC) interface standard,
        an embedded MMC (eMMC) interface standard,
        a Thunderbolt interface standard,
        a UFS interface standard,
        a Secure Digital (SD) interface standard,
        a Memory Stick interface standard,
        an xD-picture card interface standard,
        an Integrated Drive Electronics (IDE) interface standard,
        a Serial Advanced Technology Attachment (SATA) interface standard,
        an external SATA (eSATA) interface standard,
        a Small Computer System Interface (SCSI) interface standard,
        a Serial Attached Small Computer System Interface (SAS) interface standard,
        a Fibre Channel interface standard,
        an Ethernet interface standard, and
        a Peripheral Component Interconnect express (PCIe) interface standard.
    
    


EC138) Any of the foregoing ECs having a flash memory interface, wherein the flash memory interface is compatible with one or more of

    
    
        an Open NAND Flash Interface (ONFI),
        a Toggle-mode interface,
        a Double-Data-Rate (DDR) synchronous interface,
        a DDR2 synchronous interface;
        a synchronous interface, and
        an asynchronous interface.
    
    


EC139) Any of the foregoing ECs having a computing host, wherein the computing host comprises one or more of

    
    
        a computer,
        a workstation computer,
        a server computer,
        a storage server,
        a Storage Attached Network (SAN),
        a Network Attached Storage (NAS) device,
        a Direct Attached Storage (DAS) device,
        a storage appliance,
        a Personal Computer (PC),
        a laptop computer,
        a notebook computer,
        a netbook computer,
        a tablet device or computer,
        an ultrabook computer,
        an electronic reading device (an e-reader),
        a Personal Digital Assistant (PDA),
        a navigation system,
        a (handheld) Global Positioning System (GPS) device,
        an automotive control system,
        an automotive media control system or computer,
        a printer, copier or fax machine or all-in-one device,
        a Point Of Sale POS device,
        a cash-register,
        a media player,
        a television,
        a media recorder,
        a Digital Video Recorder (DVR),
        a digital camera,
        a cellular handset,
        a cordless telephone handset, and
        an electronic game.
    
    


EC140) Any of the foregoing ECs having a at least one flash memory, wherein at least a portion of the at least one flash memory comprises one or more of

    
    
        NAND flash technology storage cells, and
        NOR flash technology storage cells.
    
    


EC141) Any of the foregoing ECs having a at least one flash memory, wherein at least a portion of the at least one flash memory comprises one or more of

    
    
        Single-Level Cell (SLC) flash technology storage cells, and
        Multi-Level Cell (MLC) flash technology storage cells.
    
    


EC142) Any of the foregoing ECs having a at least one flash memory, wherein at least a portion of the at least one flash memory comprises one or more of

    
    
        polysilicon technology-based charge storage cells, and
        silicon nitride technology-based charge storage cells.
    
    


EC143) Any of the foregoing ECs having a at least one flash memory, wherein at least a portion of the at least one flash memory comprises one or more of

    
    
        two-dimensional technology-based flash memory technology, and
        three-dimensional technology-based flash memory technology.

System

    
    


FIG. 1A illustrates selected details of an embodiment of a Solid-State Disk (SSD) including an SSD controller using dynamic higher-level redundancy mode management with independent silicon elements for accessing and controlling NVMs. The SSD controller is for managing non-volatile storage, such as implemented via NVM elements (e.g., flash memories). SSD Controller 100 is communicatively coupled via one or more External Interfaces 110 to a host (not illustrated). According to various embodiments, External Interfaces 110 are one or more of: a SATA interface; a SAS interface; a PCIe interface; a Fibre Channel interface; an Ethernet Interface (such as 10 Gigabit Ethernet); a non-standard version of any of the preceding interfaces; a custom interface; or any other type of interface used to interconnect storage and/or communications and/or computing devices. For example, in some embodiments, SSD Controller 100 includes a SATA interface and a PCIe interface.
SSD Controller 100 is further communicatively coupled via one or more Device Interfaces 190 to NVM 199 including one or more storage devices, such as one or more of Flash Device 192. According to various embodiments, Device Interfaces 190 are one or more of: an asynchronous interface; a synchronous interface; a single-data-rate (SDR) interface; a double-data-rate (DDR) interface; a DRAM-compatible DDR or DDR2 synchronous interface; an ONFI compatible interface, such as an ONFI 2.2 or ONFI 3.0 compatible interface; a Toggle-mode compatible flash interface; a non-standard version of any of the preceding interfaces; a custom interface; or any other type of interface used to connect to storage devices.
Each Flash Device 192 has, in some embodiments, one or more individual Flash Die 194. According to type of a particular one of Flash Device 192, a plurality of Flash Die 194 in the particular Flash Device 192 is optionally and/or selectively accessible in parallel. Flash Device 192 is merely representative of one type of storage device enabled to communicatively couple to SSD Controller 100. In various embodiments, any type of storage device is usable, such as an SLC NAND flash memory, MLC NAND flash memory, NOR flash memory, flash memory using polysilicon or silicon nitride technology-based charge storage cells, two- or three-dimensional technology-based flash memory, read-only memory, static random access memory, dynamic random access memory, ferromagnetic memory, phase-change memory, racetrack memory, or any other type of memory device or storage medium.
According to various embodiments, Device Interfaces 190 are organized as: one or more busses with one or more of Flash Device 192 per bus; one or more groups of busses with one or more of Flash Device 192 per bus, where busses in a group are generally accessed in parallel; or any other organization of one or more of Flash Device 192 onto Device Interfaces 190.
Continuing in FIG. 1A, SSD Controller 100 has one or more modules, such as Host Interfaces 111, Data Processing 121, Buffer 131, Map 141, Recycler 151, ECC 161, Device Interface Logic 191, and CPU 171. The specific modules and interconnections illustrated in FIG. 1A are merely representative of one embodiment, and many arrangements and interconnections of some or all of the modules, as well as additional modules not illustrated, are conceived. In a first example, in some embodiments, there are two or more Host Interfaces 111 to provide dual-porting. In a second example, in some embodiments, Data Processing 121 and/or ECC 161 are combined with Buffer 131. In a third example, in some embodiments, Host Interfaces 111 is directly coupled to Buffer 131, and Data Processing 121 optionally and/or selectively operates on data stored in Buffer 131. In a fourth example, in some embodiments, Device Interface Logic 191 is directly coupled to Buffer 131, and ECC 161 optionally and/or selectively operates on data stored in Buffer 131.
Host Interfaces 111 sends and receives commands and/or data via External Interfaces 110, and, in some embodiments, tracks progress of individual commands via Tag Tracking 113. For example, the commands include a read command specifying an address (such as an LBA) and an amount of data (such as a number of LBA quanta, e.g., sectors) to read; in response the SSD provides read status and/or read data. For another example, the commands include a write command specifying an address (such as an LBA) and an amount of data (such as a number of LBA quanta, e.g., sectors) to write; in response the SSD provides write status and/or requests write data and optionally subsequently provides write status. For yet another example, the commands include a de-allocation command (e.g. a trim command) specifying one or more addresses (such as one or more LBAs) that no longer need be allocated; in response the SSD modifies the map accordingly and optionally provides de-allocation status. In some contexts an ATA compatible TRIM command is an exemplary de-allocation command For yet another example, the commands include a super capacitor test command or a data hardening success query; in response, the SSD provides appropriate status. In some embodiments, Host Interfaces 111 is compatible with a SATA protocol and, using NCQ commands, is enabled to have up to 32 pending commands, each with a unique tag represented as a number from 0 to 31. In some embodiments, Tag Tracking 113 is enabled to associate an external tag for a command received via External Interfaces 110 with an internal tag used to track the command during processing by SSD Controller 100.
According to various embodiments, one or more of: Data Processing 121 optionally and/or selectively processes some or all data sent between Buffer 131 and External Interfaces 110; and Data Processing 121 optionally and/or selectively processes data stored in Buffer 131. In some embodiments, Data Processing 121 uses one or more Engines 123 to perform one or more of: formatting; reformatting; transcoding; and any other data processing and/or manipulation task.
Buffer 131 stores data sent to/from External Interfaces 110 from/to Device Interfaces 190. In some embodiments, Buffer 131 additionally stores system data, such as some or all map tables, used by SSD Controller 100 to manage one or more of Flash Device 192. In various embodiments, Buffer 131 has one or more of: Memory 137 used for temporary storage of data; DMA 133 used to control movement of data to and/or from Buffer 131; and ECC-X 135 used to provide higher-level error correction and/or redundancy functions; and other data movement and/or manipulation functions. An example of a higher-level redundancy function is a RAID-like capability (e.g. RASIE), where redundancy is at a flash device (e.g., multiple ones of Flash Device 192) level and/or a flash die (e.g., Flash Die 194) level instead of at a disk level.
According to various embodiments, one or more of: ECC 161 optionally and/or selectively processes some or all data sent between Buffer 131 and Device Interfaces 190; and ECC 161 optionally and/or selectively processes data stored in Buffer 131. In some embodiments, ECC 161 is used to provide lower-level error correction and/or redundancy functions, such as in accordance with one or more ECC techniques. In some embodiments, ECC 161 implements one or more of: a CRC code; a Hamming code; an RS code; a BCH code; an LDPC code; a Viterbi code; a trellis code; a hard-decision code; a soft-decision code; an erasure-based code; any error detecting and/or correcting code; and any combination of the preceding. In some embodiments, ECC 161 includes one or more decoders (such as LDPC decoders).
Device Interface Logic 191 controls instances of Flash Device 192 via Device Interfaces 190. Device Interface Logic 191 is enabled to send data to/from the instances of Flash Device 192 according to a protocol of Flash Device 192. Device Interface Logic 191 includes Scheduling 193 to selectively sequence control of the instances of Flash Device 192 via Device Interfaces 190. For example, in some embodiments, Scheduling 193 is enabled to queue operations to the instances of Flash Device 192, and to selectively send the operations to individual ones of the instances of Flash Device 192 (or Flash Die 194) as individual ones of the instances of Flash Device 192 (or Flash Die 194) are available.
Map 141 converts between data addressing used on External Interfaces 110 and data addressing used on Device Interfaces 190, using Table 143 to map external data addresses to locations in NVM 199. For example, in some embodiments, Map 141 converts LBAs used on External Interfaces 110 to block and/or page addresses targeting one or more Flash Die 194, via mapping provided by Table 143. For LBAs that have never been written since drive manufacture or de-allocation, the map points to a default value to return if the LBAs are read. For example, when processing a de-allocation command, the map is modified so that entries corresponding to the de-allocated LBAs point to one of the default values. In various embodiments, there are various default values, each having a corresponding pointer. The plurality of default values enables reading some de-allocated LBAs (such as in a first range) as one default value, while reading other de-allocated LBAs (such as in a second range) as another default value. The default values, in various embodiments, are defined by flash memory, hardware, firmware, command and/or primitive arguments and/or parameters, programmable registers, or various combinations thereof.
In some embodiments, Map 141 uses Table 143 to perform and/or to look up translations between addresses used on External Interfaces 110 and data addressing used on Device Interfaces 190. According to various embodiments, Table 143 is one or more of: a one-level map; a two-level map; a multi-level map; a map cache; a compressed map; any type of mapping from one address space to another; and any combination of the foregoing. According to various embodiments, Table 143 includes one or more of: static random access memory; dynamic random access memory; NVM (such as flash memory); cache memory; on-chip memory; off-chip memory; and any combination of the foregoing.
In some embodiments, Recycler 151 performs garbage collection. For example, in some embodiments, instances of Flash Device 192 contain blocks that must be erased before the blocks are re-writeable. Recycler 151 is enabled to determine which portions of the instances of Flash Device 192 are actively in use (e.g., allocated instead of de-allocated), such as by scanning a map maintained by Map 141, and to make unused (e.g., de-allocated) portions of the instances of Flash Device 192 available for writing by erasing them. In further embodiments, Recycler 151 is enabled to move data stored within instances of Flash Device 192 to make larger contiguous portions of the instances of Flash Device 192 available for writing.
In some embodiments, instances of Flash Device 192 are selectively and/or dynamically configured, managed, and/or used to have one or more bands for storing data of different types and/or properties. A number, arrangement, size, and type of the bands are dynamically changeable. For example, data from a computing host is written into a hot (active) band, while data from Recycler 151 is written into a cold (less active) band. In some usage scenarios, if the computing host writes a long, sequential stream, then a size of the hot band grows, whereas if the computing host does random writes or few writes, then a size of the cold band grows.
CPU 171 controls various portions of SSD Controller 100. CPU 171 includes CPU Core 172. CPU Core 172 is, according to various embodiments, one or more single-core or multi-core processors. The individual processors cores in CPU Core 172 are, in some embodiments, multi-threaded. CPU Core 172 includes instruction and/or data caches and/or memories. For example, the instruction memory contains instructions to enable CPU Core 172 to execute programs (e.g. software sometimes called firmware) to control SSD Controller 100. In some embodiments, some or all of the firmware executed by CPU Core 172 is stored on instances of Flash Device 192 (as illustrated, e.g., as Firmware 106 of NVM 199 in FIG. 1B).
In various embodiments, CPU 171 further includes: Command Management 173 to track and control commands received via External Interfaces 110 while the commands are in progress; Buffer Management 175 to control allocation and use of Buffer 131; Translation Management 177 to control Map 141; Coherency Management 179 to control consistency of data addressing and to avoid conflicts such as between external data accesses and recycle data accesses; Device Management 181 to control Device Interface Logic 191; Identity Management 182 to control modification and communication of identify information, and optionally other management units. None, any, or all of the management functions performed by CPU 171 are, according to various embodiments, controlled and/or managed by hardware, by software (such as firmware executing on CPU Core 172 or on a host connected via External Interfaces 110), or any combination thereof.
In some embodiments, CPU 171 is enabled to perform other management tasks, such as one or more of: gathering and/or reporting performance statistics; implementing SMART; controlling power sequencing, controlling and/or monitoring and/or adjusting power consumption; responding to power failures; controlling and/or monitoring and/or adjusting clock rates; and other management tasks.
Various embodiments include a computing-host flash memory controller that is similar to SSD Controller 100 and is compatible with operation with various computing hosts, such as via adaptation of Host Interfaces 111 and/or External Interfaces 110. The various computing hosts include one or any combination of a computer, a workstation computer, a server computer, a storage server, a SAN, a NAS device, a DAS device, a storage appliance, a PC, a laptop computer, a notebook computer, a netbook computer, a tablet device or computer, an ultrabook computer, an electronic reading device (such as an e-reader), a PDA, a navigation system, a (handheld) GPS device, an automotive control system, an automotive media control system or computer, a printer, copier or fax machine or all-in-one device, a POS device, a cash-register, a media player, a television, a media recorder, a DVR, a digital camera, a cellular handset, a cordless telephone handset, and an electronic game.
In various embodiments, all or any portions of an SSD controller (or a computing-host flash memory controller) are implemented on a single IC, a single die of a multi-die IC, a plurality of dice of a multi-die IC, or a plurality of ICs. For example, Buffer 131 is implemented on a same die as other elements of SSD Controller 100. For another example, Buffer 131 is implemented on a different die than other elements of SSD Controller 100.
FIG. 1B illustrates selected details of various embodiments of systems including one or more instances of the SSD of FIG. 1A. SSD 101 includes SSD Controller 100 coupled to NVM 199 via Device Interfaces 190. The figure illustrates various classes of embodiments: a single SSD coupled directly to a host, a plurality of SSDs each respectively coupled directly to a host via respective external interfaces, and one or more SSDs coupled indirectly to a host via various interconnection elements.
As an example embodiment of a single SSD coupled directly to a host, one instance of SSD 101 is coupled directly to Host 102 via External Interfaces 110 (e.g. Switch/Fabric/Intermediate Controller 103 is omitted, bypassed, or passed-through). As an example embodiment of a plurality of SSDs each coupled directly to a host via respective external interfaces, each of a plurality of instances of SSD 101 is respectively coupled directly to Host 102 via a respective instance of External Interfaces 110 (e.g. Switch/Fabric/Intermediate Controller 103 is omitted, bypassed, or passed-through). As an example embodiment of one or more SSDs coupled indirectly to a host via various interconnection elements, each of one or more instances of SSD 101 is respectively coupled indirectly to Host 102. Each indirect coupling is via a respective instance of External Interfaces 110 coupled to Switch/Fabric/Intermediate Controller 103, and Intermediate Interfaces 104 coupling to Host 102.
Some of the embodiments including Switch/Fabric/Intermediate Controller 103 also include Card Memory 112C coupled via Memory Interface 180 and accessible by the SSDs. In various embodiments, one or more of the SSDs, the Switch/Fabric/Intermediate Controller, and/or the Card Memory are included on a physically identifiable module, card, or pluggable element (e.g. I/O Card 116). In some embodiments, SSD 101 (or variations thereof) corresponds to a SAS drive or a SATA drive that is coupled to an initiator operating as Host 102.
Host 102 is enabled to execute various elements of Host Software 115, such as various combinations of OS 105, Driver 107, Application 109, and Multi-Device Management Software 114. Dotted-arrow 107D is representative of Host Software ←→ I/O Device Communication, e.g. data sent/received to/from one or more of the instances of SSD 101 and from/to any one or more of OS 105 via Driver 107, Driver 107, and Application 109, either via Driver 107, or directly as a VF.
OS 105 includes and/or is enabled to operate with drivers (illustrated conceptually by Driver 107) for interfacing with the SSD. Various versions of Windows (e.g. 95, 98, ME, NT, XP, 2000, Server, Vista, and 7), various versions of Linux (e.g. Red Hat, Debian, and Ubuntu), and various versions of MacOS (e.g. 8, 9 and X) are examples of OS 105. In various embodiments, the drivers are standard and/or generic drivers (sometimes termed “shrink-wrapped” or “pre-installed”) operable with a standard interface and/or protocol such as SATA, AHCI, or NVM Express, or are optionally customized and/or vendor specific to enable use of commands specific to SSD 101. Some drives and/or drivers have pass-through modes to enable application-level programs, such as Application 109 via Optimized NAND Access (sometimes termed ONA) or Direct NAND Access (sometimes termed DNA) techniques, to communicate commands directly to SSD 101, enabling a customized application to use commands specific to SSD 101 even with a generic driver. ONA techniques include one or more of: use of non-standard modifiers (hints); use of vendor-specific commands; communication of non-standard statistics, such as actual NVM usage according to compressibility; and other techniques. DNA techniques include one or more of: use of non-standard commands or vendor-specific providing unmapped read, write, and/or erase access to the NVM; use of non-standard or vendor-specific commands providing more direct access to the NVM, such as by bypassing formatting of data that the I/O device would otherwise do; and other techniques. Examples of the driver are a driver without ONA or DNA support, an ONA-enabled driver, a DNA-enabled driver, and an ONA/DNA-enabled driver. Further examples of the driver are a vendor-provided, vendor-developed, and/or vendor-enhanced driver, and a client-provided, client-developed, and/or client-enhanced driver.
Examples of the application-level programs are an application without ONA or DNA support, an ONA-enabled application, a DNA-enabled application, and an ONA/DNA-enabled application. Dotted-arrow 109D is representative of Application ←→ I/O Device Communication (e.g. bypass via a driver or bypass via a VF for an application), e.g. an ONA-enabled application and an ONA-enabled driver communicating with an SSD, such as without the application using the OS as an intermediary. Dotted-arrow 109V is representative of Application ←→ I/O Device Communication (e.g. bypass via a VF for an application), e.g. a DNA-enabled application and a DNA-enabled driver communicating with an SSD, such as without the application using the OS or the driver as intermediaries.
One or more portions of NVM 199 are used, in some embodiments, for firmware storage, e.g. Firmware 106. The firmware storage includes one or more firmware images (or portions thereof). A firmware image has, for example, one or more images of firmware, executed, e.g., by CPU Core 172 of SSD Controller 100. A firmware image has, for another example, one or more images of constants, parameter values, and NVM device information, referenced, e.g. by the CPU core during the firmware execution. The images of firmware correspond, e.g., to a current firmware image and zero or more previous (with respect to firmware updates) firmware images. In various embodiments, the firmware provides for generic, standard, ONA, and/or DNA operating modes. In some embodiments, one or more of the firmware operating modes are enabled (e.g. one or more APIs are “unlocked”) via keys or various software techniques, optionally communicated and/or provided by a driver.
In some embodiments lacking the Switch/Fabric/Intermediate Controller, the SSD is coupled to the host directly via External Interfaces 110. In various embodiments, SSD Controller 100 is coupled to the host via one or more intermediate levels of other controllers, such as a RAID controller. In some embodiments, SSD 101 (or variations thereof) corresponds to a SAS drive or a SATA drive and Switch/Fabric/Intermediate Controller 103 corresponds to an expander that is in turn coupled to an initiator, or alternatively Switch/Fabric/Intermediate Controller 103 corresponds to a bridge that is indirectly coupled to an initiator via an expander. In some embodiments, Switch/Fabric/Intermediate Controller 103 includes one or more PCIe switches and/or fabrics.
In various embodiments, such as some of the embodiments where Host 102 is a computing host (e.g. a computer, a workstation computer, a server computer, a storage server, a SAN, a NAS device, a DAS device, a storage appliance, a PC, a laptop computer, a notebook computer, and/or a netbook computer), the computing host is optionally enabled to communicate (e.g. via optional I/O & Storage Devices/Resources 117 and optional LAN/WAN 119) with one or more local and/or remote servers (e.g. optional Servers 118). The communication enables, for example, local and/or remote access, management, and/or usage of any one or more of SSD 101 elements. In some embodiments, the communication is wholly or partially via Ethernet. In some embodiments, the communication is wholly or partially via Fibre Channel. LAN/WAN 119 is representative, in various embodiments, of one or more Local and/or Wide Area Networks, such as any one or more of a network in a server farm, a network coupling server farms, a metro-area network, and the Internet.
In various embodiments, an SSD controller and/or a computing-host flash memory controller in combination with one or more NVMs are implemented as a non-volatile storage component, such as a USB storage component, a CF storage component, an MMC storage component, an eMMC storage component, a Thunderbolt storage component, a UFS storage component, an SD storage component, a Memory Stick storage component, and an xD-picture card storage component.
In various embodiments, all or any portions of an SSD controller (or a computing-host flash memory controller), or functions thereof, are implemented in a host that the controller is to be coupled with (e.g., Host 102 of FIG. 1B). In various embodiments, all or any portions of an SSD controller (or a computing-host flash memory controller), or functions thereof, are implemented via hardware (e.g., logic circuitry), software and/or firmware (e.g., driver software or SSD control firmware), or any combination thereof. For example, functionality of or associated with an ECC unit (such as similar to ECC 161 and/or ECC-X 135 of FIG. 1A) is implemented partially via software on a host and partially via a combination of firmware and hardware in an SSD controller. For another example, functionality of or associated with a recycler unit (such as similar to Recycler 151 of FIG. 1A) is implemented partially via software on a host and partially via hardware in a computing-host flash memory controller.
Mapping Operation
FIG. 2 illustrates selected details of an embodiment of mapping an LPN portion of an LBA. In some embodiments, a read unit is a finest granularity of an NVM that is independently readable, such as a portion of a page of the NVM. In further embodiments, the read unit corresponds to check bits (sometimes-termed redundancy) of a (lower-level) error-correcting code along with all data protected by the check bits. For example, ECC 161 of FIG. 1A implements error correction via check bits such as via an LDPC code, and a read unit corresponds to coding bits implementing the LDPC code in addition to data bits protected by the LDPC coding bits.
In some embodiments, Map 141 maps LPN 213 portion of LBA 211 to Map Info for LPN 221, such as via Table 143 (as illustrated in FIG. 1A). Map info for an LPN (such as Map Info for LPN 221) is sometimes termed a map entry. Map 141 is said to associate an LPN with a corresponding map entry. In various embodiments, mapping is via one or more associative look-ups, via one or more non-associative look-ups, and/or via one or more other techniques.
In some embodiments, SSD Controller 100 maintains one map entry for each LPN potentially and/or actively in use.
In some embodiments, Map Info for LPN 221 includes respective Read Unit Address 223 and Length in Read Units 225. In some embodiments, a length and/or a span are stored encoded, such as by storing the length as an offset from the span, e.g. in all or any portions of Length in Read Units 225. In further embodiments, a first LPN is associated with a first map entry, a second LPN (different from the first LPN, but referring to a logical page of a same size as a logical page referred to by the first LPN) is associated with a second map entry, and the respective length in read units of the first map entry is different from the respective length in read units of the second map entry.
In various embodiments, at a same point in time, a first LPN is associated with a first map entry, a second LPN (different from the first LPN) is associated with a second map entry, and the respective read unit address of the first map entry is the same as the respective read unit address of the second map entry. In further embodiments, data associated with the first LPN and data associated with the second LPN are both stored in a same physical page of a same device in NVM 199.
According to various embodiments, Read Unit Address 223 is associated with one or more of: a starting address in the NVM; an ending address in the NVM; an offset of any of the preceding; and any other techniques for identifying a portion of the NVM associated with LPN 213.
FIG. 3 illustrates selected details of an embodiment of accessing an NVM at a read unit address to produce read data organized as various read units, collectively having a length measured in quanta of read units. According to various embodiments, First Read Unit 313 is one or more of: a one of read units in Read Data 311 with a lowest address in an address space of the NVM; a fixed one of the read units; an arbitrary one of the read units; a variable one of the read units; and a one of the read units selected by any other technique. In various embodiments, SSD Controller 100 is enabled to access NVM 199 and produce Read Data 311 by reading no more than a number of read units specified by Length in Read Units 225.
FIG. 4A illustrates selected details of an embodiment of a read unit (such as Read Units 313 or 315 of FIG. 3) as Read Unit 401A. In various embodiments and/or usage scenarios, Header 1 411A through Header N 419A are contiguous, and respective data regions identified (such as via respective offsets) by each of the headers are contiguous following a last one of the headers. The data regions collectively form Data Bytes 421A. The data regions are stored in a location order that matches the location order the headers are stored. For example, consider a first header, at the beginning of a read unit, with a second header and a third header contiguously following the first header. A first data region (identified by a first offset in the first header) contiguously follows the third header. A second data region (identified by a second offset in the second header) contiguously follows the first data region. Similarly, a third data region (identified by the third header) contiguously follows the second data region.
FIG. 4B illustrates selected details of another embodiment of a read unit (such as Read Units 313 or 315 of FIG. 3) as Read Unit 401B. In various embodiments and/or usage scenarios, Header Marker (HM) 410B is an optional initial field (such as a one-byte field) indicating a number of following contiguous headers (Header 1 411B, Header 2 412B . . . Header N 419B). Data regions (Data Bytes 421B, Data Bytes 422B . . . Data Bytes 429B) are identified respectively by the headers (Header 1 411B, Header 2 412B . . . Header N 419B) and are stored in a location order that is opposite of the location order that the headers are stored. Headers start at the beginning of a read unit, while corresponding data regions start at the end of a read unit. In some embodiments, data bytes within a data region (e.g. Data Bytes 421B, Data Bytes 422B . . . Data Bytes 429B) are arranged in a forward order (byte order matching location order), while in other embodiments, the data bytes are arranged in a reverse order (byte order reversed with respect to location order). In some embodiments, a header marker is used in read units where headers and data bytes are stored in a same location order (e.g. as illustrated in FIG. 4A).
In some embodiments, Optional Padding Bytes 431A (or 431B) are according to granularity of data associated with a particular LPN. For example, in some embodiments, if Data Bytes 421A (or collectively Data Bytes 421B, Data Bytes 422B . . . Data Bytes 429B) have less than a fixed amount of remaining space, such as 8 bytes, after storing data associated with all but a last one of Header 1 411A through Header N 419A (or Header 1 411B, Header 2 412B . . . Header N 419B), then data for an LPN associated with the last header starts in a subsequent read unit. In further embodiments, a particular offset value (e.g. all ones) in the last header indicates that the data for the LPN associated with the last header starts in the subsequent read unit.
FIG. 5 illustrates selected details of an embodiment of a header (such as any of Header 1 411A through Header N 419A of FIG. 4A or Header 1 411B through Header 419B of FIG. 4B) having a number of fields. In some embodiments, headers are fixed-length (e.g. each header is a same number of bytes long). Header 501 includes fields Type 511, Last Indicator 513, Flags 515, LPN 517, Length 519, and Offset 521. The type field identifies a category of the data bytes. For example, the type field indicates the category of the data bytes is one of host data (e.g. logical page data) or system data (e.g. map information or checkpoint information). The last field indicates that the header is the last header before the data bytes. In some embodiments with a header marker, the last field is optionally omitted. The LPN field is the LPN that the header is associated with. The LPN field enables parsing of the headers to determine a particular one of the headers that is associated with a particular LPN by, for example, searching the headers for one with an LPN field matching the particular LPN. The length field is the length, in bytes, of the data bytes (e.g. how many bytes of data there are in Data Bytes 421A associated with Header 501). In some embodiments, an offset in the offset field is rounded according to a particular granularity (e.g. 8-byte granularity).
In various embodiments, some or all information associated with a particular LPN is stored in a map entry associated with the particular LPN, a header associated with the particular LPN, or both. For example, in some embodiments, some or all of Length 519 is stored in a map entry rather than in a header.
FIG. 6 illustrates selected details of an embodiment of blocks, pages, and read units of multiple NVM devices. For example, 601, 603 . . . and 609 correspond to respective ones of one or more individual Flash Die 194, of FIG. 1A.
In some embodiments, Devices 601, 603 . . . and 609 are a portion less than all of NVM 199. For example, in various embodiments, data is striped independently across multiple groups of devices, where each of the groups of devices is independently accessible.
Each device (such as any one of Devices 601, 603 . . . and 609) provides storage organized as blocks (such as Blocks 631, 633 . . . and 639 of Device 601; Blocks 661, 663 . . . and 669 of Device 603; and so forth). In some embodiments, each device includes an integral number of blocks and a block is a smallest quantum of erasing. The blocks in turn include pages (such as Pages 621, 623 . . . and 629 of Block 631; Pages 651, 653 . . . and 659 of Block 661; and so forth). In some embodiments, each block includes an integral number of pages and a page is a smallest quantum of writing. The pages in turn include read units (such as Read Units 611, 613 . . . and 619 of Page 621; Read Units 641, 643 . . . and 649 of Page 651; and so forth). According to various embodiments, one or more of: a read unit is a smallest quantum of reading and error correction; each page includes an integral number of read units; an associated group of two or more pages includes an integral number of read units; and read units optionally and/or selectively span page boundaries. Reads and/or writes of information in the devices are performed according to an order, such as a ‘read unit first’ order or a ‘page first’ order. An example of a read unit first order for read units illustrated in the figure begins with Read Unit 611 followed by 641, . . . , 671, 613, 643, . . . , 673, and so forth, ending with 679. An example of a page first order for read units illustrated in the figure begins with Read Unit 611 followed by 613, . . . , 619, 641, 643, . . . , 649, 671, 673, and so forth, ending with 679.
In some embodiments, various NVM management functions are performed in units of R-blocks. An example of an R-block is a logical slice or section across all die of a flash memory. For example, in a flash memory having R flash die, each flash die having N blocks, each R-block is the ith block from each of the flash die taken together, for a total of N R-blocks. For another example, in a flash memory having R flash die, each with N blocks, each R-block is the ith and (i+1)th block from each of the flash die, for a total of N/2 R-blocks. For yet another example, in a flash memory having a plurality of dual plane devices, each R-block is the ith even block and the ith odd block from each of the dual plane devices.
Higher-Level Redundancy Techniques
FIG. 7A illustrates selected details of various embodiments of higher-level redundancy techniques. Flash Device(s) 720 includes 64 flash die (Flash Die 710.63, 710.62, 710.61 . . . 710.0) and communicates via Interface Channel(s) 730. Extra Flash Device(s) 740 includes up to two flash die (Flash Die 710.65 and 710.64) and communicates via Extra Interface Channel(s) 750. The flash die provide storage for higher-level redundancy information and data storage (e.g. user data and/or user free space) in a storage sub-system, such as NVM in an SSD. (Examples of ‘user data’ in contexts of redundancy information and data storage include all data other than the redundancy information stored on flash memory for later retrieval, such as operating system data, application data, SSD management data, and so forth.) Higher-level redundancy enables, e.g., recovering from intermittent or permanent failure of one or more portions of one or more flash die, such as a failure to provide error-corrected data (e.g. via lower-level ECC functions) for a read operation or failure to properly complete a write operation.
For example, each flash die (or alternatively each block or each page within each block) is operated in a context of a Redundant Array of Silicon Independent Elements (RASIE). If a failure is detected in a particular flash die (e.g. due to an ECC-uncorrectable read error of a portion of a block of the particular die), then in response, redundant information stored in others of the flash die is used to determine information that would have been provided by the particular die. In some embodiments and/or usage scenarios, sufficient redundant information is stored to enable recovery from one failure within one flash die (during a single operation). Operation in a mode that enables recovery from a single failure includes, in some embodiments, allocating and managing space equivalent to one flash die for higher-level redundancy information, and is termed ‘RASIE-1’. Operation in a mode that enables recovery from two failures includes, in some embodiments, allocating and managing space equivalent to two flash die for higher-level redundancy information, and is termed ‘RASIE-2’.
In some embodiments and/or usage scenarios, managing die-level failures is an objective, and spreading information amongst die is performed. For example, higher-level redundancy information is stored in one or more die specifically allocated solely to the higher-level redundancy information. In some embodiments and/or usage scenarios, managing block-level failures is an objective, and spreading information amongst blocks within a die is performed. For example, higher-level redundancy information is stored in one or more blocks allocated to the higher-level redundancy information, the allocation being without regard to which particular die the blocks were part of. In some embodiments and/or usage scenarios, managing particular-entity-level failures includes spreading information so that no more than N elements (e.g. 1 for RASIE-1 and 2 for RASIE-2) are in any one of the particular entities.
The higher-level redundancy information is computed and written in accordance with (user) data written to the flash die, and is thus available to provide information when a failure is detected. In various embodiments, the higher-level redundancy information is written to the flash die before, after, or in no particular time order with respect to writing of (user) data the higher-level redundancy information is associated with.
The figure illustrates various embodiments of RASIE operating modes, as summarized in the following table.












Usage
Usage of Extra



Mode
Flash Device(s) 740
Usage of Flash Device(s) 720







RASIE-1




1-0
-none-
710.63 (1 die) - redundancy




710.62 . . . 710.0 (63 die) - data




storage


1-1
710.64 (1 die) - redundancy
710.63 . . . 710.0 (64 die) - data




storage


RASIE-2


2-0
-none-
710.63, 710.62 (2 die) -




redundancy




710.61 . . . 710.0 (62 die) - data




storage


2-1
710.64 (1 die) - redundancy
710.63 (1 die) - redundancy




710.62 . . . 710.0 (63 die) - data




storage


2-2
710.65, 710.64 (2 die) -
710.63 . . . 710.0 (64 die) - data



redundancy
storage









More specifically, in RASIE-1 modes, space equivalent to one die is allocated to higher-level redundancy information. In RASIE-1 mode 1-0, Extra Flash Device(s) 740 is not used, as higher-level redundancy information is stored in one die of Flash Device(s) 720 (e.g. Flash Die 710.63), leaving 63 of the die (Flash Die 710.62 . . . 710.0) available for data storage (e.g. user data and/or user free space). In RASIE-1 mode 1-1, one die of Extra Flash Device(s) 740 is used (e.g. Flash Die 710.64), leaving all of Flash Device(s) 720 (64 die) available for data storage.
In RASIE-2 modes, space equivalent to two die is allocated to higher-level redundancy information. In RASIE-2 mode 2-0, Extra Flash Device(s) 740 is not used, as higher-level redundancy information is stored in two die of Flash Device(s) 720 (e.g. Flash Die 710.63 and Flash Die 710.62), leaving 62 of the die (Flash Die 710.61 . . . 710.0) available for data storage. In RASIE-2 mode 2-1, one die of Extra Flash Device(s) 740 is used (e.g., Flash Die 710.64), as higher-level redundancy information is partially stored in one die of Flash Device(s) 720 (e.g. Flash Die 710.63), leaving 63 of the die (Flash Die 710.62 . . . 710.0) available for data storage. In RASIE-2 mode 2-2, two die of Extra Flash Device(s) 740 are used (e.g. Flash Die 710.65 and Flash Die 710.64), leaving all of Flash Device(s) 720 (64 die) available for data storage.
In some embodiments, die that are unused in all usage scenarios are unpopulated. For example, in a system operable only in RASIE 2-0 mode and RASIE 1-0mode (but not in other RASIE modes), Extra Flash Device(s) 740 is unpopulated.
In some embodiments, higher-level redundancy information is stored entirely in “dedicated” die (e.g. flash die 710.63 in RASIE-1 mode 1-0 or Flash Die 710.65 and Flash Die 710.64 in RASIE-2 mode 2-2). In other embodiments, higher-level redundancy information is stored in any of the die, so for example, in RASIE-1 mode 1-0 Flash Die 710.62 is used for higher-level redundancy information, while Flash Die 710.63 and Flash Die 710.61 . . . 710.0 are used for data storage. In some embodiments and/or usage scenarios, higher-level redundancy information is stored in different die (and/or portions thereof) over time, so, for example, in a first time period a first flash die holds higher-level redundancy information while in a second time period a second flash die hold higher-level redundancy information.
In various embodiments, there are a plurality of RASIE 1-0 modes (and a plurality of RASIE 2-0 modes) depending on how many flash die are usable. For example, in a first RASIE 1-0 mode (as illustrated in the table above), Flash Die 710.63 stores higher-level redundancy information, and Flash Die 710.62 . . . 710.0 are available for data storage. In a second RASIE 1-0 mode, Flash Die 710.63 is no longer usable, Flash Die 710.62 stores higher-level redundancy information, and Flash Die 710.61 . . . 710.0 are available for data storage, decreasing an available amount of data storage by one die. RASIE modes where a die (or any portions thereof) previously available for data storage is no longer available for data storage due to use of the die (or the portions) for higher-level redundancy information are sometimes referred to as reduced-capacity RASIE modes.
In some embodiments, higher-level redundancy information is stored using a same and/or a similar lower-level error correction coding scheme as user data protected by the higher-level redundancy information. Using a lower-level error correction scheme to protect the higher-level redundancy information enables determining if there is an uncorrectable error in the higher-level redundancy information, in a same and/or a similar manner that an uncorrectable lower-level error in the user data is determined.
FIG. 7B illustrates selected details of an embodiment of R-blocks. Flash die are managed (e.g. for recycling and/or erasing) in logical slices or sections across all die, and the slices/sections are referred to as R-blocks. The figure illustrates an embodiment with 66 flash die (Flash Die 710.65 . . . 710.0). Blocks, pages, and management of the blocks as R-blocks are illustrated. Each flash die is illustrated as having N blocks (such as Block 710.65B0, Block 710.65B1 . . . Block 710.65BB of Flash Die 710.65). Each R-block is the ith block from each of the flash die, taken together (such as R-block 760.0 being Block 710.65B0 from Flash Die 710.65, block 0 from Flash Die 710.64 (not explicitly illustrated), and so forth to Block 710.0B0 of Flash Die 710.0. There are thus a total of N R-blocks (R-block 760.0, R-block 760.1 . . . R-block 760.R).
In various embodiments, a writing and/or a striping order of data within an R-block is page (e.g. lowest to highest) first, across all devices (e.g. lowest to highest numbered devices, as suggested conceptually by Striping Direction 600 of FIG. 6), then the next highest page (across all devices), and so forth, continuing throughout the last page of the R-block. Specifically with respect to R-block 760.0 of FIG. 7, an example order begins with Page 710.0P0, followed by the first page in the first block of Flash Die 710.1, and so forth continuing to Page 710.65P0. The example order continues with Page 710.0P1, followed by the second page in the first block of Flash Die 710.1, and so forth continuing to Page 710.65P1. The example order completes with Page 710.0PP, followed by the last page in the first block of Flash Die 710.1, and so forth ending with Page 710.65PP.
Another example of an R-block is the ith and (i+1)th block from each of the flash die, taken together (e.g. blocks 0 and 1 from Flash Die 710.65, blocks 0 and 1 from Flash Die 710.64, and so forth to blocks 0 and 1 from Flash Die 710.0). There are thus N/2 R-blocks, if there are N blocks in each flash die. Yet another example of an R-block is the ith even and odd blocks from each of a plurality of dual plane devices. Other arrangements of flash die blocks for management as R-blocks are contemplated, including mapping between virtual and physical block addresses to ensure that R-blocks have one block from each die, even if some blocks are inoperable. In various embodiments, some of the N blocks in each flash die are used as spares so that the mapping between virtual and physical block addresses has spare (otherwise unused) blocks to replace defective ones of the blocks in the R-blocks.
In various embodiments that blocks are treated in pairs or other associated groups as part of forming an R-block, respective pages from each block of an associated group of the blocks are also treated as a unit, at least for writing, forming a larger multi-block page. For example, continuing the dual plane example above, a first page of a particular one of the even blocks and a first page of an associated one of the odd blocks are treated as a unit for writing, and optionally and/or selectively as a unit for reading. Similarly, a second page of the particular even block and a second page of the associated odd block are treated as a unit. According to various embodiments, a page of NVM as used herein refers to one or more of: a single page of NVM; a multi-block page of NVM; a multi-block page of NVM for writing that is optionally and/or selectively treated as one or more individual pages for reading; and any other grouping or association of pages of NVM.
In some embodiments, higher-level redundancy information is stored in different die for different portions of data. For instance, in some embodiments where flash die are managed in R-blocks, higher-level redundancy information is stored in different flash die for different R-blocks. For example, higher-level redundancy information for an R-block including block 0 of Flash Die 710.0 is stored in Flash Die 710.0, while higher-level redundancy information for an R-block including block 1 of Flash Die 710.0 is stored in Flash Die 710.1, and so forth. In some embodiments, such as some embodiments where flash die are managed in R-blocks, higher-level redundancy information is written after data the higher-level redundancy information depends on is known and/or is written.
In some usage scenarios, one or more portions of an NVM element (e.g. a block of a device, such as Block 639 of Device 601 of FIG. 6) are, or become during operation, inoperable. In some embodiments, the inoperable portions are mapped out via virtual and physical block addresses (e.g. via processing performed via Map 141 and/or Table 143 of FIG. 1A.). Alternatively, the inoperable portions are skipped (rather than explicitly mapped out). In some embodiments based on R-blocks, the skipping results in some of the R-blocks having differing numbers of blocks. For example, if Block 710.0B0 is defective and unusable, then R-block 760.0 has one fewer block than R-block 760.1. The higher-level redundancy information is written in a (per R-block) variable location that is, for example, the last block of each R-block.
In various embodiments, one or more elements of FIG. 7A correspond to one or more elements of FIG. 1A. For example, Flash Device(s) 720 and Extra Flash Device(s) 740 collectively correspond to NVM 199, and Interface Channel(s) 730 and Extra Interface Channel(s) 750 collectively correspond to Device Interfaces 190. For another example, Flash Die 710.65 . . . 710.0 collectively correspond to the instances of Flash Die 194. For yet another example, one or more of the flash devices of Flash Device(s) 720 and/or Extra Flash Device(s) 740 correspond to one or more of the instances of Flash Devices 192. In various embodiments, one or more elements of FIG. 1A manage higher-level redundancy information and/or recover user data based at least in part on the higher-level redundancy information in accordance with the RASIE operating modes described herein. For example, a portion of software execution capabilities of CPU 171 is used to manage computation of higher-level redundancy information according to various RASIE operating modes. For another example, Data Processing 121 and/or ECC-X 135 includes hardware elements dedicated to and/or specialized for computation of higher-level redundancy information and/or recovery of user data according to various RASIE operating modes. For yet another example, ECC 161 detects an ECC-uncorrectable (lower-level) read error of a portion of a flash die, and ECC-X 135 detects a RASIE (higher-level) read error and/or enables correction thereof.
In various embodiments, Interface Channel(s) 730 variously has one, four, eight, or 16 channels, and Extra Interface Channel(s) 750 variously has one or two channels. In various embodiments, Flash Device(s) 720 is implemented as one, two, four, eight, or 16 devices, each having respectively 64, 32, 16, eight, and four of the flash die. In various embodiments, Extra Flash Device(s) 740 is implemented as one device having one or two die or as two devices each having one die. In some embodiments, the flash die of Extra Flash Device(s) 740 are implemented in devices that also implement the flash die of Flash Device(s) 720. For example, one flash device implements 66 flash die (Flash Die 710.65 . . . 710.0). For another example, two flash devices each implement 33 flash die, e.g. in a first flash device (Flash Die 710.65 . . . 710.33) and in a second flash device (Flash Die 710.32 . . . 710.0). Other arrangements of flash die and flash devices are contemplated. In some embodiments having Extra Flash Device(s) 740 implemented in devices that also implement flash die of Flash Device(s) 720, the flash die communicate via shared interface channels, or alternatively via interface channels dedicated to particular ones (or sets) of the flash die. While Flash Device(s) 720 and Extra Flash Device(s) 740 are illustrated with specific numbers of flash die (2 and 64, respectively), other embodiments are contemplated, such as Flash Device(s) 720 having 2, 4, 8, 16, 32, or 128 flash die, and/or Extra Flash Device(s) 740 having 0, 1, or 4 flash die.
FIG. 8 illustrates selected details of an embodiment of dynamic higher-level redundancy mode management with RASIE, such as dynamically switching between RASIE modes enabled by the various embodiments illustrated by FIG. 7A and/or FIG. 7B. In some embodiments and/or usage scenarios, a form of graceful degradation is provided where a storage sub-system (e.g. an SSD) is dynamically transitioned from operating in first higher-level redundancy mode to operating in a second higher-level redundancy mode. The transition is in response to detection of a failure, such as a permanent or intermittent malfunction of an entire flash die or one or more portions thereof, or an operation (such as a read or write operation) thereto. According to various embodiments, the transition is one or more of: global for the SSD; performed on one or more subsets of the SSD; and performed on one or more R-blocks of the SSD. For example, if a particular block of one of the NVM devices storing RASIE-2 information fails during programming, then subsequent operation of the R-block containing the particular (failed) block transitions to a different higher-level redundancy mode (e.g. a RASIE-1 mode), whereas other R-blocks in the SSD are unaffected and continue to operate in the RASIE-2 mode.
With respect to FIG. 8, processing begins with higher-level redundancy information and data storage (e.g. user data and/or user free space) arranged in flash die in accordance with a first higher-level redundancy mode (Operate in First Higher-Level Redundancy Mode 802). Flow then proceeds to determine if a failure has been detected (Failure? 803), such as a lower-level uncorrectable read error or a write/program failure. If no failure has been detected, then flow proceeds back to continue operation in the first higher-level redundancy mode. If a failure has been detected, then flow proceeds to switch from operating in the first higher-level redundancy mode to operating in a second higher-level redundancy mode. The switch begins by (optionally) decreasing space available for data storage (Reduce Free Space 804) to account for the failure. If the second higher-level redundancy mode uses sufficiently less higher-level redundancy information than the first higher-level redundancy mode, then the decreasing of available space is omitted. The switch continues by reorganizing data storage in accordance with the second higher-level redundancy mode (Rearrange Data Storage 805). The reorganizing includes optionally moving all user data and/or user free space from the flash die where the failure occurred to another one of the flash die (user free space movement is accomplished, in some embodiments, by manipulation of pointers and/or other data structure elements). The switch further continues by selectively restoring (if possible), via the higher-level redundancy information of the first higher-level redundancy mode, any user data that was stored in the flash die where the failure occurred, and writing the restored user data to another one of the flash die, in accordance with the second higher-level redundancy mode (Recover/Store Failed User Data 806). The restoring is omitted if the failure is a write/program failure. The switch further continues by optionally computing and writing to the flash die higher-level redundancy information in accordance with the second higher-level redundancy mode (Determine/Store Revised Higher-Level Redundancy Information 807). The computing and the writing are omitted if the second higher-level redundancy mode is operable with higher-level redundancy information that was previously in place due to operating in the first higher-level redundancy mode. Then operation begins in the second higher-level redundancy mode (Operate in Second Higher-Level Redundancy Mode 808).
The failure detection (Failure? 803) is via one or more of: lower-level error correction (e.g. in accordance with one or more ECC techniques), higher-level error correction (e.g. in accordance with one or more RASIE techniques), and failing status reported by one or more of the flash die or portions thereof. For example, more than a threshold number of lower-level corrections of reads within a particular portion of a particular flash die optionally and/or conditionally results in the particular flash die (or the particular portion) being treated as failed and a higher-level redundancy mode switch is performed so that the failed flash die (or portion) is no longer used. For another example, if a higher-level error correction fails, then an appropriate one of the flash die (or portion thereof) is treated as failed and a higher-level redundancy mode switch is performed so that the failed flash die (or portion) is no longer used. For yet another example, if a flash die returns a program failure status (indicating that a write operation was unsuccessful), then an appropriate block of an appropriate one of the flash die is treated as failed, and optionally and/or conditionally a higher-level redundancy mode switch is performed so that the failed flash die is no longer used.
In some embodiments, a failed block is replaced by remapping via virtual and physical block addresses (e.g. via processing performed via Map 141 and/or Table 143 of FIG. 1A). A spare block from a pool of spare blocks is mapped in place of the failed block. Any contents written in the failed block are copied to the replacement block, and writing proceeds in the spare block from where the failure occurred in the failed block.
In some embodiments, a failed block is skipped (rather than explicitly remapped), resulting in a “hole” that optionally and/or conditionally results in a higher-level redundancy mode switch when the R-block that the hole is in is next erased (in preparation for re-writing). If the hole is in a location for data storage, then no switch is made, and the hole remains. If the hole is in a location for higher-level redundancy information, then the higher-level redundancy information is stored in another location, and optionally the higher-level redundancy mode is switched.
In some embodiments and/or usage scenarios, restoration of user data stored in the flash die where the failure occurred is not possible. For example, if the failure is due to some types of failures detected via higher-level error correction and/or some types of failing status reported by one or more of the flash die or portions thereof, then some user data may be lost.
In some embodiments, processing of FIG. 8 is performed in a context of (e.g. an SSD controller) dynamically transitioning between higher-level redundancy modes in response to a plurality of failures. Specifically, the SSD controller begins operating in a first higher-level redundancy mode and dynamically transitions to a second higher-level redundancy mode in response to a first failure, and subsequently dynamically transitions from the second higher-level redundancy mode to a third higher-level redundancy mode in response to a second failure, and so forth. For instance, an SSD controller operates various flash die in accordance with a RASIE-2 mode 2-2 and dynamically transitions the operation to be in accordance with a RASIE-2 mode 2-1 in response to a first failure. Subsequently, the SSD controller dynamically transitions the operation to be in accordance with a RASIE-2 mode 2-0 in response to a second failure. Further subsequently, the SSD controller dynamically transitions the operation to be in accordance with a RASIE-1 reduced-capacity mode 1-0 in response to a third failure (the reduced-capacity mode 1-0 being similar to RASIE-1 mode 1-0 except with one flash die used for higher-level redundancy information and 62 flash die used for data storage).
As a specific example, consider an SSD controller (such as SSD Controller 100 of FIG. 1A) coupled to the elements of FIG. 7A, initially operating in RASIE-2 mode 2-2 (e.g. higher-level redundancy information in Flash Die 710.65 and Flash Die 710.64, and data storage in Flash Die 710.63 . . . 710.0), corresponding to operating in the first higher-level redundancy mode. Then a read, or alternatively a write, of one or more of the flash die is performed. The read results in an uncorrectable (lower-level) ECC failure, or alternatively the write is unsuccessful, in a portion of a particular one of the flash die (e.g. a page of Flash Die 710.62 used for user data and/or user free space). In response, the SSD controller dynamically switches from operating in RASIE-2 mode 2-2 to RASIE-2 mode 2-1, no longer using any of Flash Die 710.62. As operation in RASIE-2 mode 2-1 provides 63 die for data storage (versus 64 die in RASIE-2 mode 2-2), space available for data storage is decreased from 64 die to 63 die, and user data and/or user free space is moved accordingly. E.g., all user data from Flash Die 710.62 is moved to portions of Flash Die 710.63 and Flash Die 710.61 . . . 710.0 in accordance with user free space. Any user data in the page having the uncorrectable ECC failure is recovered based on the higher-level redundancy information in Flash Die 710.65 and/or Flash Die 710.64. Higher-level redundancy information based on data storage in Flash Die 710.63 and Flash Die 710.61 . . . 710.0 and in accordance with RASIE-2 mode 2-1 is computed and stored in Flash Die 710.65 and/or Flash Die 710.64. The SSD controller then operates in RASIE-2 mode 2-1 (higher-level redundancy information in Flash Die 710.65 and flash die 710.64, and data storage in Flash Die 710.63 and Flash Die 710.61 . . . 710.0).
While the foregoing described several embodiments of dynamic higher-level redundancy mode management with independent silicon elements of a granularity of an entire flash die, other embodiments implement dynamic higher-level redundancy mode management with independent silicon elements that are portions of a die, such as one or more pages, blocks, or R-blocks.
In various embodiments, processing of or relating to one or more elements of FIG. 8 is performed entirely or in part by one or more elements (or portions thereof) of FIG. 1A. For example, a portion of software execution capabilities of CPU 171 is used to manage dynamic transitioning between higher-level redundancy modes, such as by directing decreasing space available for data storage or directing reorganizing data storage. For another example, Data Processing 121 and/or ECC-X 135 includes hardware elements dedicated to and/or specialized for computation of higher-level redundancy information in accordance with a ‘target’ redundancy mode. For yet another example, ECC 161 implements lower-level (e.g. ECC) error correction and detection of uncorrectable errors, while ECC-X 135 implements higher-level (e.g. RASIE) error correction and detection of uncorrectable errors and/or memory element failures. For another example, all or any portions of functionality relating to dynamic transitioning between (higher-level) redundancy modes is performed by one or more portions of ECC-X 135.
Higher-Level Redundancy and Adaptive Lower-Level Code Rates
In some embodiments and/or usage scenarios, lower-level error correction uses an adaptive code rate (e.g. an adaptive ECC technique using a variable code rate). For instance, a first read unit is managed with a first code rate that provides relatively more usable data bits than a second read unit that is managed with a second code rate. In some embodiments and/or usage scenarios with lower-level error correction using a variable code rate, higher-level redundancy information is stored in portions of independent silicon elements (such as portions of flash die) that are managed with lower-level error correction that provides relatively more usable data bits or the most usable data bits with respect to data storage protected by the higher-level redundancy information. The portion(s) where the higher-level redundancy information is stored varies, in various embodiments and/or usage scenarios, on a per R-block basis, on a per-die basis, dynamically over time, or any combination thereof. In various embodiments, one or more die, R-blocks, blocks, and/or pages are selected for storage of higher-level redundancy data based on having the most usable data with respect to lower-level error correction code rate.
For example, higher-level redundancy information is stored at varying locations (such as block locations) on a per R-block basis, the locations (such as blocks) being those having the most usable data based on lower-level error correction code rate. In an arbitrary example, consider a RASIE-2 operating mode scenario in the context of FIG. 7A, wherein the collection of 66 flash die is treated as a logical “stack” of up to M R-blocks of one-block height each, where M is the number of blocks per flash die. (In the most conceptually straightforward case, each R-block in the stack is made up of the same physical block number from each die, but to accommodate failed blocks this constraint is lifted in at least some embodiments. In yet other embodiments, the constraint is maintained, but “holes” are accommodated corresponding to the failed blocks.) Thus, each R-block has up to 66 blocks, corresponding to one block from each of Flash Die 710.0 through Flash Die 710.65. (In FIG. 7A, while only some flash die in the range 710.0 through 710.65 are explicitly enumerated, it is understood by the use of ellipsis that all flash die in this range are implicitly illustrated.) The higher-level redundancy information is written into whichever blocks of each R-block have the most useable data based on lower-level correction code rate. If for example in a first R-block, blocks corresponding to Flash Die 710.15 and 710.49 happen to have the most usable data based on lower-level error correction code rate, then higher-level redundancy information is written into those blocks (corresponding to Flash Die 710.15 and 710.49). While if in a second R-block, blocks corresponding to flash die 710.9 and 710.35 happen to have the most usable data based on lower-level error correction code rate, then higher-level redundancy information is written into those blocks (corresponding to Flash Die 710.9 and 710.35). In some embodiments, the higher-level redundancy data is written after all other data in an R-block is known.
FIG. 9 illustrates an embodiment of Read Units (911, 931 . . . 951, 971) having lower-level redundancy information of adaptive (e.g. differing and/or varying over time and/or by location) code rates protected by higher-level redundancy information stored in one or more of the read units. Each of the read units has a portion enabled and/or allocated to contain User Data (911.U, 931.0 . . . 951.U, 971.U), and a remaining portion enabled and/or allocated to contain lower-level redundancy information, such as check bits of an ECC code as Lower-Level ECC (911.E, 931.E . . . 951.E, 971.E).
In the figure, vertical dimensions are relatively to scale and indicative of relative size. Thus Read Units 911 and 951 are of a same first size (in some embodiments, all read units are a same size for all blocks of all NVM devices), Lower-Level ECC portions 931.E and 951.E are of a same second size, and Lower-Level ECC portions 911.E and 971.E are of a same third size. Read Unit 931 is larger than Read Units 911 and 951 that are in turn larger than Read Unit 971. User Data portion 931.0 is larger than User Data portion 951.U. User Data portion 951.0 is larger than User Data portion 911.U. Lower-Level ECC portion 951.E is smaller than Lower-Level ECC portion 911.E.
As illustrated in the figure, respective read units have respective sizes, e.g. per respective block of NVM, enabling varying lower-level code rates as used in the respective blocks. More specifically, Read Units 931 and 951 have a same amount of lower-level redundancy information (931.E and 951.E are a same size), but a lower-level code rate of Read Unit 931 is higher than a lower-level code rate of Read Unit 951, as Read Unit 931 contains more User Data (931.U) than Read Unit 951 (containing User Data 951.U).
As illustrated in the figure, respective read units have respective sizes of user data, enabling various sizes of user data in each of two or more read units of a same size. For example, a size of user data is varied to change a lower-level code rate used in a particular read unit. More specifically, Read Units 951 and 911 have a same size, but have different respective amounts of User Data (951.0 and 911.U), and thus different respective amounts of lower-level redundancy information (951.E and 911.E), enabling Read Unit 951 to have a higher lower-level code rate than Read Unit 911.
In some embodiments and/or usage scenarios, varying and/or changing a lower-level code rate advantageously enables providing a sufficient amount of lower-level ECC information to achieve lower-level error correction requirements while maximizing an amount of user data.
In some embodiments with a varying amount of user data in read units, higher-level redundancy information is stored in a one or more of the read units having a largest amount of user data. For example in FIG. 9, using a RASIE-1 mode, higher-level redundancy information is stored in User Data 931.U, and using a RASIE-2 mode, higher-level redundancy information is stored in User Data 931.0 and User Data 951.U. Storing the higher-level redundancy information in read units with the largest amount of user data (among the read units protected by the higher-level redundancy information) ensures that there is sufficient higher-level redundancy information to protect the user data in all of the other read units.
According to various embodiments, one or more techniques are used to determine which of one or more read units among a number of read units protected by higher-level redundancy information are used to store higher-level redundancy information. In a first example, the latest-written one (for RASIE-1) or two (for RASIE-2) read units that have a largest amount of user data are used. In a second example, the earliest-written one (for RASIE-1) or two (for RASIE-2) read units that have a largest amount of user data are used. Similarly, any technique to deterministically select one or more read units having a largest amount of user data so as to protect all of the remaining user data in the other read units is within the scope of the techniques considered herein.
Higher-Level Redundancy Information Computation Techniques
In various embodiments and/or usage scenarios, higher-level redundancy information is computed with a variety of techniques, such as via parity, RS, and/or weighted-sum techniques. For example, in some higher-level redundancy modes enabling recovery from one (lower-level) failure (e.g. RASIE-1), higher-level redundancy information is computed via parity techniques. For another example, in some higher-level redundancy modes enabling recovery from two (lower-level) failures (e.g. RASIE-2), higher-level redundancy information is computed via a combination of parity and RS techniques. A first portion of the higher-level redundancy information is computed using parity coding and a second portion is computing using RS coding. For yet another example, in some higher-level redundancy modes enabling recovery from two failures (e.g. RASIE-2), higher-level redundancy information is computed via a combination of parity and weighted-sum techniques. A first portion of the higher-level redundancy information is computed using parity coding and a second portion is computing using weighted-sum coding. The higher-level redundancy information is managed, e.g. via reads and writes of pages of NVM, using lower-level failure detection techniques (such as ECC) identical to or similar to lower-level failure detection techniques used for pages of the NVM available for storing data protected by the higher-level redundancy information.
As a specific example for RASIE-2, a first page of higher-level redundancy information is computed using parity coding via an XOR of all first pages in a stripe across an R-block. More specifically, an XOR is performed of all of the first bytes of all of the first pages in the stripe across the R-block, resulting in a first byte of the first page of higher-level redundancy information. Similarly, a second byte of higher-level redundancy information is formed by XORing all of the second bytes of all of the first pages in the stripe across the R-block, and so forth for all of the bytes of all of the first pages in the stripe. A second page of higher-level redundancy information is computed using a weighted-sum technique as follows.
Arithmetic is performed over a finite field, such as a Galois Field (used as an example). Examples assume data being operated on is byte-wide, and thus a field such as GF(256) is used. In various embodiments, data is operated on in any units.
Each page in a stripe is assigned a unique non-zero “index”. The values of the indices are chosen to simplify implementation complexity, and are not related to any form of generator polynomial. For example, the pages are labeled (e.g. by software) by die location in a stripe from 0 to N−1, and a suitable value for the indices is the ones-complement of the die number (ensured to be non-zero provided N<255). Another selection of index values is the lowest-weight (fewest number of set bits or fewest number of clear bits) non-zero integers, e.g. to reduce and/or minimize hardware costs. Selecting gray-coded values for the indices, in some embodiments and/or usage scenarios, minimizes transitions and/or reduces power as pages are processed.
The index values are not selected according to finite field arithmetic, but are selected according to other principles. Notwithstanding this, each index value corresponds to a non-zero element in the finite field. Assume that page i has index value Ki (and page j has index value Kj). The weighted-sum redundancy is the (GF field) sum (over corresponding bytes Pi from each page i) of Ki*Pi, each byte multiplied (over the GF field) by its index value.
Thus weighted-sum redundancy information is computed for each byte as:

    
    
        R0=sum over all corresponding bytes Pi;
        R1=sum over all corresponding bytes Ki*Pi;
        R0 is the XOR of all the corresponding bytes; and
        R1 is a weighted sum of the bytes, where the weights are selected as the index values.

The foregoing computation is iterated for each of the corresponding bytes in a page, producing corresponding pages of bytes for each of R0 and R1. In the following discussion, R0 and R1 are described in some contexts respectively as single elements (e.g. each being a single byte) for clarity of exposition, but as in the foregoing computation, each are representative of a respective page of elements (e.g. each being a page of bytes).

    
    


Pi represents a byte in page i, and Pj represents a byte in page j. Processing is described with respect to one stripe of corresponding bytes from each page, and iteration is performed over all corresponding bytes. If some pages are “shorter” than others, due to for example to having a different (lower-level) redundancy code rate, then the shorter pages are zero-padded (or padded by any known value used the same way on encode and decode) so that all pages that are processed effectively have the same size.
Summations to compute R0 and R1 are performable in any order, via various serial and/or parallel computations, according to various embodiments. Pages do not have to be processed in any specific order as whether Ki*Pi is added in prior to or subsequent to Kj*Pj has no effect on the result in R1. Computation of R0 and R1 values corresponding to various bytes of a page of redundancy information are independent of each other and are computable in any order, via various serial and/or parallel computations, according to various embodiments. Further, subtracting Ki*Pi from R1 (and subtracting Pi from R0) enables “backing out” of computation effects on pages. Since over a GF field, addition and subtraction are both XOR (thus subtracting is equivalent to simply adding in a second time), in some embodiments and/or usage scenarios, no special hardware is needed for GF field implementations (e.g. a logical XOR capability is sufficient) to “back out” a page.
In the event of an uncorrectable lower-level error, higher-level correction begins, in some embodiments, by re-computing R0 and R1, but by omitting page(s) (sometimes referred to as column(s)) that have uncorrectable lower-level errors. Correction proceeds by subtracting the recomputed R0 from the original R0 to produce ΔR0, and subtracting the recomputed R1 from the original R1 to produce ΔR1.
If there are no uncorrectable lower-level errors, then the recomputed R0 and R1 are both zero. If there are uncorrectable lower-level errors, then the recomputed R0 and R1 (after the subtraction) reflect the “missing” data (that was not added in the second time, but was present in the original values).
If there is one uncorrectable lower-level error, then the recomputed R0 is used to correct the error (and the recomputed R1 is not needed).
If there are two uncorrectable lower-level errors, then the recomputed R0 and R1 are used to correct the errors. If both the pages of R0 and R1 values are the pages with uncorrectable lower-level errors, then no correction of data storage pages is needed. If the page of R1 values is one of the pages with uncorrectable lower-level errors, then correction is via R0 (the recomputed R0 value is the value of the data storage page with uncorrectable lower-level errors).
If there are two uncorrectable lower-level errors in data storage pages, or if the R0 page is one of the pages with uncorrectable lower-level errors, then correction starts by computing ΔR0 and ΔR1 as above. If the R0 page is one of the pages with uncorrectable lower-level errors, computation of the ΔR0 page is optionally omitted. If page i and page j are pages with uncorrectable lower-level errors, then the recomputed ΔR0=Pi+Pj, and the recomputed ΔR1=Ki*Pi+Kj*Pj. Equation solving produces:

Pi=(ΔR1−Kj*ΔR0)/(Ki−Kj)

Pj=ΔR0−Pi 

If R0 is one of the pages with uncorrectable lower-level errors, then (because R0 is not included in R1), ΔR1=Ki*Pi, or Pi=ΔR1/Ki; the same result obtained by setting Kj=0 in the formulas above (to ignore ΔR0).

In an alternative embodiment, a finite field defined by integers mod p, where p is a prime, is used instead of a Galois Field. The computations are identical to those described above, with addition being integer addition mod p, and multiplication being integer multiplication mod p. For example, if pages are pages of bytes, a finite field of integers mod 257 is used. All user data bytes are in a range 0-255 and are stored in one byte each. R1 results, however, have values ranging from 0-256, requiring more than one byte for representation. There are many ways to encode values from 0-256 to minimize storage space and enable the R1 page to be stored with reduced overhead. For example, values 0 and 256 are stored as nine-bit sequences 000000000 and 000000001 respectively, and all other values are stored in eight bits. Given a random distribution of R1 values, storage overhead is <0.1%. As described with respect to FIG. 9, the R1 page is selected to have a largest amount of user data, enabling the storage overhead to be hidden in some usage scenarios.
FIG. 10 illustrates selected details of an embodiment of higher-level redundancy information result and data source correspondences, for instance as used by RASIE-2 mode 2-2 in a context such as FIG. 7A and as further illustrated in FIG. 7B. FIG. 10 explicitly illustrates Flash Die 710.0, 710.63, 710.64 and, 710.65, and by ellipsis ( . . . ) implicitly illustrates Flash Die 710.1 . . . 710.62. Selected details of blocks, pages, and bytes within pages of the flash die are illustrated. A first portion of higher-level redundancy information is illustrated as R0 1010 (stored in Flash Die 710.64), and is computed using parity coding. A second portion of higher-level redundancy information is illustrated as R1 1011 (stored in Flash Die 710.65), and is computed using weighted-sum coding. Storage for data information is illustrated as Data 1019 (stored in Flash Die 710.0 . . . 710.63).
Dashed-arrow 1001 conceptually indicates a two-byte redundancy computation result (one byte for each of R0 1010 and R1 1011) based on corresponding first bytes of all first pages (across all flash die) of Data 1019. As illustrated, the two-byte result is the first byte on each of the first R0 and R1 pages. Dashed arrow 1002 conceptually indicates a two-byte redundancy computation result (one byte for each of R0 1010 and R1 1011) based on corresponding last bytes of all first pages of Data 1019. As illustrated, the two-byte result is the last byte on each of the first R0 and R1 pages. Dashed-arrow 1003 conceptually indicates a two-page redundancy computation result (one page for each of R0 1010 and R1 1011) based on corresponding last pages of the first blocks (across all flash die) of Data 1019.
Note that as described elsewhere herein, in some embodiments higher-level redundancy information is stored in different die for different portions of data. Thus, R0 and R1, in some embodiments, are stored across various die, rather than two “dedicated” die, as illustrated in FIG. 10.
FIG. 11 illustrates selected details of an embodiment of higher-level redundancy information computations, for instance as used by RASIE-2 mode 2-2 in a context such as FIG. 7A and as further illustrated in FIG. 7B and FIG. 10, with various operating conditions according to various embodiments. More specifically, FIG. 11 illustrates parity coding computation for a byte of R0 and weighted-sum coding computation for a byte of R1, in accordance with, e.g., the two-byte redundancy computation result illustrated conceptually by dashed-arrow 1001 of FIG. 10. The operating conditions include one or more of: performing arithmetic over a finite field (such as a Galois Field), indices (corresponding to dummy summation variable “i” values in FIG. 11) being ones-complement of flash die number (or any other unique and non-zero numbering), and indices corresponding to non-zero elements in the finite field. The computation as illustrated in FIG. 11 is repeated for all of the bytes of R0 and R1, based on the corresponding data bytes. Note that non-zero indices enable R1 values to include a contribution from every element of Pi.
Thus there are no dependencies on computing any of the bytes of R0 on each other or between any of the bytes of R1. Therefore various embodiments are contemplated where R0 and R1 values are computed entirely (massively) in parallel, partially in parallel, or entirely in serial. For example, all of the R0 and/or R1 bytes of a page are computed in parallel. For another example, all of the R0 bytes of a page are computed in parallel followed (or preceded) by computing in parallel all of the R1 bytes of a page.
Further, there are no ordering requirements on computing any of the bytes of R0 with respect to each other or with respect to computing any of the bytes of R1. Therefore various embodiments are contemplated where R0 and R1 values are computed entirely in-order with respect to each other, in-order with respect to each other separately (e.g. R0 computations are in-order with respect to each other but with no ordering with respect to R1, and vice-versa), or with no particular ordering (e.g. entirely out-of-order, unordered, or randomly ordered). For example, all of the R0 bytes of a page are computed in a particular order (e.g. from lowest byte to highest byte), followed by all of the R1 bytes of the page in the particular order. For another example, all of the R0 bytes of a page are computed in the particular order, and independently all of the R1 bytes of the page are computed in the particular order. For yet another example, all of the R0 bytes of a page as well as all of the R1 bytes of a page are computed in no particular order with respect to each other (e.g. as data operands become available).
For yet another example, all of the R0 and R1 bytes of one or more pages are computed in an order determined by an order of completion of one or more read operations performed on one or more NVMs (each having, e.g., one or more flash die), the read operations for reading the data bytes referenced by the summation and weighted-summation computations (Pi) illustrated in FIG. 11. Performing the computations in the order determined by the completion of the read operations enables, in some embodiments and/or usage scenarios, reduction or elimination of buffering between the NVMs and elements enabled to perform the computations. Performing the computations in the order determined by the completion of the read operations enables, in some embodiments and/or usage scenarios, reduction in memory bandwidth used to perform the computations, such as memory bandwidth of the NVMs.
For yet another example, all of the R0 and R1 bytes of one or more pages are computed in an order determined by an order of data returned and/or data available in response to read operations performed on one or more NVMs (each having, e.g., one or more flash die), the data returned and/or data available corresponding to the data bytes referenced by the summation and weighted-summation computations (Pi) illustrated in FIG. 11. In some embodiments and/or usage scenarios, performing the computations in the order determined by the data returned and/or data available reduces or eliminates buffering between the NVMs and elements enabled to perform the computations. In some embodiments and/or usage scenarios, performing the computations in the order determined by the data returned and/or data available reduces memory bandwidth used to perform the computations, such as memory bandwidth of the NVMs. In some embodiments, the read operations are performed in a particular order (e.g. from lowest byte to highest byte of Pi), while in other embodiments, the read operations are performed in no particular order.
FIG. 12 illustrates selected details of an embodiment of recovery from one (lower-level) failure (during a single operation), for instance in a context such as associated with FIG. 11, and where the lower-level failure has occurred on page j. Note that if the lower-level failure is on an R0 or an R1 page, then R0 (or R1) is re-determined as described by FIG. 11. FIG. 12 illustrates a computation for one byte of a recovered value for page j (note that the summation omits page j where the failure occurred). The computation as illustrated in FIG. 12 is repeated to determine recovered values for all of the bytes of page j, based on corresponding bytes of R0 and corresponding bytes from all of the data pages except for page j.
Thus there are no dependencies on computing any of the bytes of the recovered values of page j on each other. Therefore various embodiments are contemplated where Pj recovery values are computed ranging from highly parallel to highly serial, similarly to the aforementioned computations for R0 and R1 values. Further, there are no order requirements on computing any of the recovery values of page j with respect to each other. Therefore various embodiments are contemplated where Pj recovery values are computed in varying orderings with respect to each other, similarly to the aforementioned computations for R0 and R1 values.
Some exemplary embodiments perform computations related to determining recovery values in orderings at least in part determined by ordering of completion of one or more read operations performed on one or more NVMs (each having, e.g., one or more flash die), the read operations for reading the NVMs to obtain R0 and/or Pi values as illustrated by FIG. 12. Performing the computations in the order of the completion of the read operations enables, in some embodiments and/or usage scenarios, reduction or elimination of buffering between the NVMs and elements enabled to perform the computations. Performing the computations in the order of the completion of the read operations enables, in some embodiments and/or usage scenarios, reduction in memory bandwidth used to perform the computations, such as memory bandwidth of the NVMs.
Some exemplary embodiments perform computations related to determining recovery values in orderings at least in part determined by ordering of data returned and/or data available from one or more NVMs (each having, e.g., one or more flash die), the data returned and/or data available being in response to read operations performed on the NVMs to obtain R0 and/or Pi values as illustrated by FIG. 12. In some embodiments and/or usage scenarios, performing the computations in the order of the data returned and/or data available from the read operations reduces or eliminates buffering between the NVMs and elements enabled to perform the computations. In some embodiments and/or usage scenarios, performing the computations in the order of the data returned and/or data available from the read operations reduces memory bandwidth used to perform the computations, such as memory bandwidth of the NVMs. In some embodiments, the read operations are performed in a particular order (e.g. from lowest byte to highest byte of Pi), while in other embodiments, the read operations are performed in no particular order.
FIGS. 13A-13D illustrate selected details of an embodiment of recovery from two (lower-level) failures (during a single operation), for instance in a context such as associated with FIG. 11, and where the lower-level failures have occurred on pages m and n. Note that if the lower-level failures are on R0 and R1 pages, then R0 and R1 are unneeded for data recovery, and there is no processing to recover data. Otherwise, note that if one of the lower-level failures is an R1 page, then data recovery proceeds as described by FIG. 12. If neither of the lower-level failures are on R0 or R1 pages, then recovery of Pm and Pn values proceeds as follows. FIG. 13A illustrates computations for one byte of a revised R0 as R0′ and for one byte of a revised R1 as R1′ (note that the summations omit pages m and n where the failures occurred). FIG. 13B illustrates equalities relating one byte of the original redundancy information (R0, R1) to the revised redundancy information (R0′, R1′), and the terms omitted from the summations used to form the revised R0 and R1 (Pm+Pn and Km*Pm+Kn*Pn). FIG. 13C illustrates an algebraic rearrangement of FIG. 13B, with introduced terms delta R0 (ARO) and delta R1 (AR1). FIG. 13D illustrates a solution of FIG. 13C for Pn and Pm, and thus represents computations for one byte of a recovered value for page n and one byte of a recovered value for page m, based on the corresponding bytes of R1, R0, and corresponding bytes from all of the data pages except for pages m and n. Note that unique indices enable a non-zero denominator, as Kn is unique with respect to Km.
In various embodiments, computations as represented by FIGS. 13A-13D are performed to determine one byte of a recovered value for page m and one byte of a recovered value for page n. The computations are repeated to determine recovered values for all of the bytes of pages m and n, based on corresponding bytes of R0, R1, and corresponding bytes from all of the data pages except for pages m and n.
Thus there are no dependencies on computing any of the bytes of the recovered values of pages m or n on each other. Therefore various embodiments are contemplated where Pm and/or Pn recovery values are computed ranging from highly parallel to highly serial, similarly to the aforementioned computations for Pj recovery values. Further, there are no order requirements on computing any of the recovery values of page m and/or page n with respect to each other. Therefore various embodiments are contemplated where Pm and/or Pn recovery values are computed in varying orderings with respect to each other, similarly to the aforementioned computations for Pj recovery values.
Some exemplary embodiments perform computations related to determining recovery values (such as computations for R0′ and R1′) in orderings at least in part determined by ordering of completion of one or more read operations performed on one or more NVMs (each having, e.g., one or more flash die), the read operations to obtain any one or more of values illustrated as sources for computations in any of FIGS. 13A-13D. Performing the computations in the order of the completion of the read operations enables, in some embodiments and/or usage scenarios, reduction or elimination of buffering between the NVMs and elements enabled to perform the computations. Performing the computations in the order of the completion of the read operations enables, in some embodiments and/or usage scenarios, reduction in memory bandwidth used to perform the computations, such as memory bandwidth of the NVMs.
Some other exemplary embodiments perform computations related to determining recovery values (such as computations for R0′ and R1′) in orderings at least in part determined by ordering of data returned and/or data available from one or more NVMs (each having, e.g., one or more flash die), the data returned and/or data available being in response to read operations performed on the NVMs to obtain any one or more of values illustrated as sources for computations in any of FIGS. 13A-13D. In some embodiments and/or usage scenarios, performing the computations in the order of the data returned and/or data available from the read operations reduces or eliminates buffering between the NVMs and elements enabled to perform the computations. In some embodiments and/or usage scenarios, performing the computations in the order of the data returned and/or data available from the read operations reduces memory bandwidth used to perform the computations, such as memory bandwidth of the NVMs. In some embodiments, the read operations are performed in a particular order (e.g. from lowest byte to highest byte of Pi), while in other embodiments, the read operations are performed in no particular order.
FIGS. 14A and 14B illustrate selected details of an embodiment of computing higher-level redundancy information with respect to pages received from NVMs. FIG. 14A illustrates selected details of an embodiment of sending a plurality of read commands to one or more NVMs via issuing (Issue Read Operation 1402A), checking if all of the commands have been sent (All Issued? 1403A), and if not, then looping back to send another of the commands Note that other embodiments are contemplated where a plurality of commands are issued at a time, rather than one at a time.
FIG. 14B illustrates selected details of an embodiment of processing pages received from the NVMs in response to the read commands sent as illustrated in FIG. 14A. A check is made to determine if a page is available (Page Ready? 1402B). If not, then processing loops back to perform the check again. If a page is available, then higher-level redundancy information processing relating to the page is carried out (Perform Page-Based Computations 1403B). Then a check is made to determine if all pages have been processed (Pages Finished? 1404B). If so, then processing is complete (End 1499B), otherwise flow loops back to determine if another page is available.
Other than reception of pages in response to the commands sent as illustrated in FIG. 14A, the processing illustrated in FIG. 14B is independent of processing illustrated in FIG. 14A. In various scenarios, arrival order of the pages varies according to the NVM type, state, operating environment, and other factors, and in some circumstances is different than sending order or arrival order of the read commands corresponding to the arriving pages. As processing of FIG. 14A is independent of FIG. 14B (other than page data arrival being dependent on a corresponding read command being sent), in some embodiments and/or usage scenarios, read commands are being sent (FIG. 14A) while read data is being received/processed (FIG. 14B). In some embodiments and/or usage scenarios, some of the pages are provided from one or more buffers rather than being requested via read commands directed to the NVMs, for example if a particular page is present in a particular buffer before a read command for the particular page is to be sent. In some embodiments and/or usage scenarios, pages other than in response to the commands sent are provided by the NVMs intermixed with the pages provided in response to the commands sent, e.g. pages provided in response to read commands sent for other activities.
In various embodiments, computations for R0 and R1, as illustrated by FIG. 11, are performed at least in part as illustrated by FIGS. 14A and 14B. For a first example, read commands for all data pages necessary to compute corresponding R0 and R1 pages are sent to one or more NVMs as illustrated by FIG. 14A. The pages of data received in response to the read commands are processed as the pages are received to compute the R0 and the R1 pages, as illustrated by FIG. 11. For a second example, read commands for a pair (corresponding, e.g., to two planes of a dual-plane NVM) of R0 and R1 pages are sent to one or more NVMs as illustrated by FIG. 14A. The pages of data received in response to the read commands are processed as the pages are received to compute the R0 and the R1 pages, as illustrated by FIG. 11.
In various embodiments, computations for Pj, as illustrated by FIG. 12, are performed at least in part as illustrated by FIGS. 14A and 14B. For a first example, read commands for all data pages necessary to compute a particular Pj page are sent to one or more NVMs as illustrated by FIG. 14A. The pages of data received in response to the read commands are processed as the pages are received to compute the Pj page, as illustrated by FIG. 12. For a second example, read commands for a pair of Pj pages (corresponding, e.g., to two planes of a dual-plane NVM) are sent to one or more NVMs as illustrated by FIG. 14A, and the pages of data received are processed as received, as illustrated by FIG. 14B, to compute the pair of Pj pages.
In various embodiments, computations related to determining recovery values (such as computations for R0′ and R1′), as illustrated by any of FIGS. 13A-13D, are performed at least in part as illustrated by FIGS. 14A and 14B. For a first example, read commands for all data pages necessary to compute a particular R0′ page and a particular R1′ are sent to one or more NVMs as illustrated by FIG. 14A. The pages of data received in response to the read commands are processed as the pages are received to compute the R0′ and R1′ pages, as illustrated by FIG. 13A. For a second example, read commands for a pair of R0′ and R1′ pages (corresponding, e.g., to two planes of a dual-plane NVM) are sent to one or more NVMs as illustrated by FIG. 14A, and the pages of data received are processed as received, as illustrated by FIG. 14B, to compute the pair of R0′ and R1′ pages.
FIGS. 15A-15C illustrate selected details of an embodiment of backing out of a computation of higher-level redundancy information with respect to a write provided to NVMs, for instance in a context such as associated with FIG. 11. FIG. 15A illustrates selected details of an embodiment of sending a plurality of write commands to one or more NVMs via issuing (Issue Write Operation 1502A), checking if all of the commands have been sent (All Issued? 1503A), and if not, then looping back to send another of the commands Note that other embodiments are contemplated where a plurality of commands are issued at a time, rather than one at a time.
FIG. 15B illustrates selected details of an embodiment of processing write completion and status information received from the NVMs in response to the write commands sent as illustrated in FIG. 15A. A check is made to determine if a write has completed without errors (Write OK? 1502B). If so, then a check is made to determine if all writes have been completed (Writes Finished? 1504B). If so, then processing is complete (End 1599B). If a write has been completed but with a (lower-level) error such as a program failure, then the flow proceeds to “undo” the effect of the write with respect to higher-level redundancy information computation (Backout Write from Redundancy 1503B). More specifically, data for the write with the lower-level error is de-computed from any corresponding higher-level redundancy information computations (assuming that the data for the write had already been included in the corresponding higher-level redundancy computations under a presumption that the write would succeed). For example, a lower-level write failure is detected on a particular page j. In response, revised R0 and R1 pages are computed such that page j data (Pj) is set to zero. FIG. 15C illustrates selected details of an embodiment of a computation for a single byte of a revised R0 (nR0) and a single byte of a revised R1 (nR1), where j is the page of the lower-level write failure. Note that in contexts of FIG. 12 such as associated with FIG. 11, if the finite field is a Galois Field the subtraction operation (“−”) illustrated in FIG. 15C is equivalent to a logical XOR operation. Other processing (not illustrated) is performed, in various embodiments, to store the page with the lower-level write failure (Pj), as well as the revised higher-level redundancy pages (nR0 and nR1).
Other than reception of write completion and status information in response to the commands sent as illustrated in FIG. 15A, the processing illustrated in FIG. 15B is independent of processing illustrated in FIG. 15A. In various scenarios, arrival order of the write completion and status information varies according to the NVM type, state, operating environment, and other factors, and in some circumstances is different than sending order or arrival order of the write commands corresponding to the arriving write completion and status information. As processing of FIG. 15A is independent of FIG. 15B (other than write completion and status information arrival being dependent on a corresponding write command being sent), in some embodiments and/or usage scenarios, write commands are being sent (FIG. 15A) while write completion and status information is being received/processed (FIG. 15B).
In some embodiments and/or usage scenarios, a significant latency transpires between write commands being sent to the NVMs and reception of write completion and status information from the NVMs in response to the write commands In some embodiments and/or usage scenarios, write completion and status information other than in response to the commands sent as illustrated in FIG. 15A are provided by the NVMs intermixed with the write completion and status information provided in response to the commands sent as illustrated in FIG. 15A, e.g. write completion and status information provided in response to write commands sent for other activities.
In various embodiments and/or usage scenarios, one or more pages that would otherwise be used for data information are unused. In various scenarios an unused page is a first, middle, or last page of a block, R-block, stripe, or sequence of pages any kind. In some circumstances, unused pages are unused a priori (“left out”), and in some circumstances unused pages are unused after some use (“removed from service”). An example of an unused page that is left out is a page that is manufactured incorrectly. An example of an unused page that is removed from service is a page that fails to write properly (e.g. as described as a lower-level write error with respect to FIG. 15B). Processing, e.g. relating to FIGS. 10-12, 13A-13D, 14A-14B, and 15A-15B, skips over any unused pages (whether left out or removed from service), such as by omitting the unused pages entirely from computations, or by performing computations as if all data on the unused pages were zero.
In various embodiments, processing of or relating to one or more elements of FIGS. 10-12, 13A-13D, 14A-14B, and 15A-15B is performed entirely or in part by one or more elements (or portions thereof) of FIG. 1A. For example, a portion of software execution capabilities of CPU 171 is used to manage higher-level redundancy processing, such as by directing data recovery operations as illustrated by FIG. 12 and FIGS. 13A-13D. For another example, Data Processing 121 includes hardware elements dedicated to and/or specialized for computation of higher-level redundancy information in accordance with computations such as illustrated by FIG. 11.
EXAMPLE IMPLEMENTATION TECHNIQUES
In some embodiments, various combinations of all or portions of operations performed by a system implementing dynamic higher-level redundancy mode management, such as with independent silicon elements (e.g. flash memories), a computing-host flash memory controller, and/or an SSD controller (such as SSD Controller 100 of FIG. 1A), and portions of a processor, microprocessor, system-on-a-chip, application-specific-integrated-circuit, hardware accelerator, or other circuitry providing all or portions of the aforementioned operations, are specified by a specification compatible with processing by a computer system. The specification is in accordance with various descriptions, such as hardware description languages, circuit descriptions, netlist descriptions, mask descriptions, or layout descriptions. Example descriptions include: Verilog, VHDL, SPICE, SPICE variants such as PSpice, IBIS, LEF, DEF, GDS-II, OASIS, or other descriptions. In various embodiments, the processing includes any combination of interpretation, compilation, simulation, and synthesis to produce, to verify, or to specify logic and/or circuitry suitable for inclusion on one or more integrated circuits. Each integrated circuit, according to various embodiments, is designable and/or manufacturable according to a variety of techniques. The techniques include a programmable technique (such as a field or mask programmable gate array integrated circuit), a semi-custom technique (such as a wholly or partially cell-based integrated circuit), and a full-custom technique (such as an integrated circuit that is substantially specialized), any combination thereof, or any other technique compatible with design and/or manufacturing of integrated circuits.
In some embodiments, various combinations of all or portions of operations as described by a computer readable medium having a set of instructions stored therein, are performed by execution and/or interpretation of one or more program instructions, by interpretation and/or compiling of one or more source and/or script language statements, or by execution of binary instructions produced by compiling, translating, and/or interpreting information expressed in programming and/or scripting language statements. The statements are compatible with any standard programming or scripting language (such as C, C++, Fortran, Pascal, Ada, Java, VBscript, and Shell). One or more of the program instructions, the language statements, or the binary instructions, are optionally stored on one or more computer readable storage medium elements. In various embodiments some, all, or various portions of the program instructions are realized as one or more functions, routines, sub-routines, in-line routines, procedures, macros, or portions thereof.
Conclusion
Certain choices have been made in the description merely for convenience in preparing the text and drawings and unless there is an indication to the contrary the choices should not be construed per se as conveying additional information regarding structure or operation of the embodiments described. Examples of the choices include: the particular organization or assignment of the designations used for the figure numbering and the particular organization or assignment of the element identifiers (the callouts or numerical designators, e.g.) used to identify and reference the features and elements of the embodiments.
The words “includes” or “including” are specifically intended to be construed as abstractions describing logical sets of open-ended scope and are not meant to convey physical containment unless explicitly followed by the word “within.”
Although the foregoing embodiments have been described in some detail for purposes of clarity of description and understanding, the invention is not limited to the details provided. There are many embodiments of the invention. The disclosed embodiments are exemplary and not restrictive.
It will be understood that many variations in construction, arrangement, and use are possible consistent with the description, and are within the scope of the claims of the issued patent. For example, interconnect and function-unit bit-widths, clock speeds, and the type of technology used are variable according to various embodiments in each component block. The names given to interconnect and logic are merely exemplary, and should not be construed as limiting the concepts described. The order and arrangement of flowchart and flow diagram process, action, and function elements are variable according to various embodiments. Also, unless specifically stated to the contrary, value ranges specified, maximum and minimum values used, or other particular specifications (such as flash memory technology types; and the number of entries or stages in registers and buffers), are merely those of the described embodiments, are expected to track improvements and changes in implementation technology, and should not be construed as limitations.
Functionally equivalent techniques known in the art are employable instead of those described to implement various components, sub-systems, operations, functions, routines, sub-routines, in-line routines, procedures, macros, or portions thereof. It is also understood that many functional aspects of embodiments are realizable selectively in either hardware (i.e., generally dedicated circuitry) or software (i.e., via some manner of programmed controller or processor), as a function of embodiment dependent design constraints and technology trends of faster processing (facilitating migration of functions previously in hardware into software) and higher integration density (facilitating migration of functions previously in software into hardware). Specific variations in various embodiments include, but are not limited to: differences in partitioning; different form factors and configurations; use of different operating systems and other system software; use of different interface standards, network protocols, or communication links; and other variations to be expected when implementing the concepts described herein in accordance with the unique engineering and business constraints of a particular application.
The embodiments have been described with detail and environmental context well beyond that required for a minimal implementation of many aspects of the embodiments described. Those of ordinary skill in the art will recognize that some embodiments omit disclosed components or features without altering the basic cooperation among the remaining elements. It is thus understood that much of the details disclosed are not required to implement various aspects of the embodiments described. To the extent that the remaining elements are distinguishable from the prior art, components and features that are omitted are not limiting on the concepts described herein.
All such variations in design are insubstantial changes over the teachings conveyed by the described embodiments. It is also understood that the embodiments described herein have broad applicability to other computing and networking applications, and are not limited to the particular application or industry of the described embodiments. The invention is thus to be construed as including all possible modifications and variations encompassed within the scope of the claims of the issued patent.

## Claims

1. A method comprising:
computing k redundant data portions to protect n-k data information portions;
storing each of the k redundant data portions and each of the n-k data information portions in separate corresponding areas, each of the corresponding areas in a respective one of n physical devices, the k redundant portions including a first parity code data and a second parity code data both associated with a first data information portion of the data information portions, the first parity code data and the second parity code data stored separately and computed using different coding, wherein the first parity code data and the second parity code data are stored on different physical devices of the n physical devices, wherein the first parity code data is computed using multiple exclusive-OR (XOR) operations, wherein the second parity code data is computed as a weighted sum of data, where weights are selected as index values;
subsequent to a failure such that one of the corresponding areas is no longer usable, computing j redundant data portions to protect n-1-j data information portions; and
wherein j<=k.

2. The method of claim 1, wherein the computing k redundant data portions to protect n-k data information portions operates in a first data protection mode, the computing j redundant data portions to protect n-1-j data information portions operates in a second data protection mode, and further comprising, in response to the failure, switching from operating in the first data protection mode to operating in the second data protection mode.

3. The method of claim 1, wherein when j==k, a total amount of the data information portions is decreased and a degree of protection is at least preserved.

4. The method of claim 3, wherein the degree of protection is protection against failures of up to j of the corresponding areas.

5. The method of claim 1, wherein when j==k-1 and j>=1, a total amount of the data information portions is preserved, a degree of protection is decreased, and the data information portions are protected.

6. The method of claim 5, wherein the decreased degree of protection is protection against failures of up to j-1 of the corresponding areas.

7. The method of claim 1,
wherein each of the n physical devices comprises a plurality of the corresponding areas; further comprising storing, in each of a plurality of sets of the corresponding areas, a respective set of data comprising a data information subset and a redundant data subset protecting the data information subset, the redundant data subset stored in distinct ones of the n physical devices from the data information subset; and
wherein each of the sets of the corresponding areas comprises no more than one corresponding area of each one of the n physical devices, and each of the respective sets of data is stored in a different set of n or less of the n physical devices.

8. The method of claim 7, wherein prior to the failure, the data information subset of a particular one of the sets of data comprises the n-k data information portions, and the redundant data subset of the particular set of data comprises the k redundant data portions.

9. The method of claim 7, wherein a first one of the corresponding areas in a particular one of the n physical devices is used to store a portion of the data information subset of a first one of the sets of data, and a second one of the corresponding areas in the particular physical device is used to store a portion or all of the redundant data subset of a second one of the sets of data.

10. An apparatus comprising:
a set of n physical storage devices; and
a controller coupled to each of physical storage device of the set of n physical storage devices over an interface, the controller configured to:
compute k redundant data portions to protect n-k data information portions;
store each of the k redundant data portions and each of the n-k data information portions in separate corresponding areas, each of the corresponding areas in a respective one of the n physical storage devices, the k redundant portions including a first parity code data and a second parity code data both associated with a first data information portion of the data information portions, the first parity code data and the second parity code data stored separately and computed using different coding, the first parity code data and the second parity code data stored on different physical storage devices of the n physical storage devices, the first parity code data computed using multiple exclusive-OR (XOR) operations, the second parity code data computed as a weighted sum of data, where weights are selected as index values; and
subsequent to a failure such that one of the corresponding areas is no longer usable, compute j redundant data portions to protect n-1-j data information portions, wherein j<=k.

11. The apparatus of claim 10, wherein the controller operates in a first data protection mode when computing the k redundant data portions and the controller operates in a second data protection mode when computing the j redundant data portions, and the controller is further configured to, in response to the failure, switch from operating in the first data protection mode to operating in the second data protection mode.

12. The apparatus of claim 10, wherein when j==k-1 and j>=1, a total amount of the data information portions is preserved, a degree of protection is decreased, and the data information portions are protected.

13. The apparatus of claim 12, wherein the decreased degree of protection is protection against failures of up to j-1 of the corresponding areas.

14. The apparatus of claim 10, each of the n physical devices comprising a plurality of the corresponding areas, and the controller further configured to store, in each of a plurality of sets of the corresponding areas, a respective set of data comprising a data information subset and a redundant data subset protecting the data information subset, the redundant data subset stored in distinct ones of the n physical devices from the data information subset, wherein each of the sets of the corresponding areas comprises no more than one corresponding area of each one of the n physical devices, and each of the respective sets of data is stored in a different set of n or less of the n physical devices.