# Patent

## Title
Apparatus, system, and method for indexing data of an append-only, log-based structure

## Abstract

Apparatuses, systems, and methods are disclosed for indexing data of an append-only, log-based structure. A storage controller writes a plurality of data packets to a storage medium by sequentially appending the data packets to a log-based structure of the storage medium. The data packets may be associated with different logical identifiers belonging to a logical address space that is independent of physical storage locations on the storage medium. An indexing module writes an index segment associated with the plurality of data packets to the log-based structure. The index segment may include index entries for determining the logical identifiers of the data packets. The indexing module records, on the storage medium, information indicating where the index segment is written on the storage medium.

## Background
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 61/510,952 entitled “SELF-CONTAINED INDICES TO DATA CONTENT” and filed on Jul. 22, 2011 for James Peterson, et al., which is incorporated herein by reference.


TECHNICAL FIELD
The present disclosure, in various embodiments, relates to indexing data of an append-only, log-based structure.
BACKGROUND
Typical block storage devices store data on physical media according to a block address scheme. Some storage devices may present themselves as block storage devices to which users may write data according to the block address scheme. However, these storage devices may actually store data on media according to a scheme different from the block address scheme. In doing so, a mapping may be maintained between block addresses and physical addresses. Recreating such a mapping from metadata persisted on storage media may be time consuming.



BRIEF DESCRIPTION OF THE DRAWINGS
Understanding that these drawings depict only embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the disclosure will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:
FIG. 1 is a schematic block diagram illustrating one embodiment of a system including a storage device;
FIG. 2 is a schematic block diagram illustrating one embodiment of a solid-state storage device controller for a data storage device;
FIG. 3 is a schematic block diagram illustrating one embodiment of a solid-state storage controller with a write data pipeline and a read data pipeline in a data storage device;
FIG. 4A is a schematic block diagram illustrating one embodiment of a bank interleave controller in a solid-state storage controller;
FIG. 4B is a schematic block diagram illustrating an alternate embodiment of a bank interleave controller in the solid-state storage controller;
FIG. 5 is a schematic block diagram illustrating one embodiment of a logical representation of a solid-state storage controller with a logical-to-physical translation layer;
FIG. 6 is a schematic block diagram illustrating data packets and index segments within a logical erase block; and
FIG. 7 is a schematic block diagram illustrating relationships between index segments of a logical erase block.



DETAILED DESCRIPTION
Furthermore, the described features, advantages, and characteristics of the disclosure may be combined in any suitable manner in one or more embodiments. The disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the disclosure. These features and advantages of the present disclosure will become more fully apparent from the following description and appended claims, or may be learned by the practice of the disclosure as set forth hereinafter.
Many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices, or the like.
Modules may also be implemented in software for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module.
Indeed, a module of executable code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network. Where a module or portions of a module are implemented in software, the software portions are stored on one or more computer readable media.
Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
Reference to a computer readable medium may take any form capable of storing machine-readable instructions on a digital processing apparatus. A computer readable medium may be embodied by a compact disk, digital-video disk, blu-ray disc, a magnetic tape, a Bernoulli drive, a magnetic disk, a punch card, flash memory, integrated circuits, or other digital processing apparatus memory device, but is not embodied by propagating signals.
Furthermore, the described features, structures, or characteristics of the disclosure may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments of the disclosure. However, the disclosure may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure.
The schematic flow chart diagrams included herein are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.
FIG. 1 depicts one embodiment of a system 100 for reducing data loss. In the depicted embodiment, the system 100 includes a host computing system 114 and a storage device 102. The host computing system 114 may be a computer such as a server, laptop, desktop, a mobile device, or other computing device. The host computing system 114 may include components such as memory, processors, buses, and other components.
The host computing system 114 stores data in the storage device 102 and communicates data with the storage device 102 via a communications connection. The storage device 102 may be internal to the host computing system 114 or external to the host computing system 114. The communications connection may be a bus, a network, or other manner of connection allowing the transfer of data between the host computing system 114 and the storage device 102. In one embodiment, the storage device 102 is connected to the host computing system 114 by a PCI connection such as PCI express (“PCI-e”). The storage device 102 may be a card that plugs into a PCI-e connection on the host computing system 114.
The storage device 102, in the depicted embodiment, performs data storage operations such as reads, writes, erases, etc. In certain embodiments, a power connection and the communications connection for the storage device 102 are part of the same physical connection between the host computing system 114 and the storage device 102. For example, the storage device 102 may receive power over PCI, PCI-e, serial advanced technology attachment (“serial ATA” or “SATA”), parallel ATA (“PATA”), small computer system interface (“SCSI”), IEEE 1394 (“FireWire”), Fiber Channel, universal serial bus (“USB”), PCIe-AS, or another connection with the host computing system 114.
The storage device 102 provides nonvolatile storage for the host computing system 114. FIG. 1 shows the storage device 102 as a nonvolatile solid-state storage device 102 comprising a solid-state storage controller 104, a write data pipeline 106, a read data pipeline 108, and nonvolatile solid-state storage media 110. The storage device 102 may contain additional components that are not shown in order to provide a simpler view of the storage device 102.
The solid-state storage media 110 stores data such that the data is retained even when the storage device 102 is not powered. Examples of solid-state storage media 110 include flash memory, nano random access memory (“NRAM”), magneto-resistive RAM (“MRAM”), dynamic RAM (“DRAM”), phase change RAM (“PRAM”), Racetrack memory, Memristor memory, nanocrystal wire-based memory, silicon-oxide based sub-10 nanometer process memory, graphene memory, Silicon-Oxide-Nitride-Oxide-Silicon (“SONOS”), Resistive random-access memory (“RRAM”), programmable metallization cell (“PMC”), conductive-bridging RAM (“CBRAM”), and the like. While, in the depicted embodiment, the storage device 102 includes solid-state storage media 110, in other embodiments, the storage device 102 may include another type of non-volatile storage media 110. For example, in certain embodiments, the storage media 110 of the storage device 102 may include magnetic media such as hard disks, tape, and the like, optical media, or other non-volatile data storage media 110. In light of this disclosure, it is clear that the description of solid-state storage media 110 herein is equally applicable to other types of storage media 110. The storage device 102 also includes a storage controller 104 that coordinates the storage and retrieval of data in the solid-state storage media 110. The storage controller 104 may use one or more indexes to locate and retrieve data, and perform other operations on data stored in the storage device 102. For example, the storage controller 104 may include a groomer for performing data grooming operations such as garbage collection.
As shown, the storage device 102, in certain embodiments, implements a write data pipeline 106 and a read data pipeline 108, an example of which is described in greater detail below. The write data pipeline 106 may perform certain operations on data as the data is transferred from the host computing system 114 into the solid-state storage media 110. These operations may include, for example, error correction code (ECC) generation, encryption, compression, and others. The read data pipeline 108 may perform similar and potentially inverse operations on data that is being read out of solid-state storage media 110 and sent to the host computing system 114.
In one embodiment, the host computing system 114 includes one or more other components in addition to the storage device 102, such as additional storage devices, graphics processors, network cards, and the like. The different types of components that may be in a host computing system 114. The components may be internal or external to the host computing system 114. In one embodiment, some of the components may be PCI or PCI-e cards that connect to the host computing system 114 and receive power through the host computing system 114.
FIG. 2 is a schematic block diagram illustrating one embodiment 200 of a solid-state storage device controller 202 that includes a write data pipeline 106 and a read data pipeline 108 in a solid-state storage device 102. The solid-state storage device controller 202 may include a number of solid-state storage controllers 0-N 104a-n, each controlling solid-state storage media 110. In the depicted embodiment, two solid-state controllers are shown: solid-state controller 0 104a and solid-state storage controller N 104n, and each controlling respective solid-state storage media 110a-n. In the depicted embodiment, solid-state storage controller 0 104a controls a data channel so that the attached solid-state storage media 110a stores data. Solid-state storage controller N 104n controls an index metadata channel associated with the stored data and the associated solid-state storage media 110n stores index metadata. In an alternate embodiment, the solid-state storage device controller 202 includes a single solid-state controller 104a with a single solid-state storage media 110a. In another embodiment, there are a plurality of solid-state storage controllers 104a-n and associated solid-state storage media 110a-n. In one embodiment, one or more solid-state controllers 104a-104n-1, coupled to their associated solid-state storage media 110a-110n-1, control data while at least one solid-state storage controller 104n, coupled to its associated solid-state storage media 110n, controls index metadata.
In one embodiment, at least one solid-state controller 104 is a field-programmable gate array (“FPGA”) and controller functions are programmed into the FPGA. In a particular embodiment, the FPGA is a Xilinx® FPGA. In another embodiment, the solid-state storage controller 104 comprises components specifically designed as a solid-state storage controller 104, such as an application-specific integrated circuit (“ASIC”) or custom logic solution. Each solid-state storage controller 104 may include a write data pipeline 106 and a read data pipeline 108, which are describe further in relation to FIG. 3. In another embodiment, at least one solid-state storage controller 104 is made up of a combination FPGA, ASIC, and custom logic components.
The solid-state storage media 110 is an array of non-volatile solid-state storage elements 216, 218, 220, arranged in banks 214, and accessed in parallel through a bi-directional storage input/output (“I/O”) bus 210. The storage I/O bus 210, in one embodiment, is capable of unidirectional communication at any one time. For example, when data is being written to the solid-state storage media 110, data cannot be read from the solid-state storage media 110. In another embodiment, data can flow both directions simultaneously. However bi-directional, as used herein with respect to a data bus, refers to a data pathway that can have data flowing in only one direction at a time, but when data flowing one direction on the bi-directional data bus is stopped, data can flow in the opposite direction on the bi-directional data bus.
A solid-state storage element (e.g., SSS 0.0 216a) may be configured as a chip (a package of one or more dies) or a die on a circuit board. As depicted, a solid-state storage element (e.g., 216a) operates independently or semi-independently of other solid-state storage elements (e.g., 218a) even if these several elements are packaged together in a chip package, a stack of chip packages, or some other package element. As depicted, a row of solid-state storage elements 216a, 216b, 216m is designated as a bank 214. As depicted, there may be “n” banks 214a-n and “m” solid-state storage elements 216a-m, 218a-m, 220a-m per bank in an array of n×m solid-state storage elements 216, 218, 220 in a solid-state storage media 110. Of course, different embodiments may include different values for n and m. In one embodiment, a solid-state storage media 110a includes twenty solid-state storage elements 216a-216m per bank 214 with eight banks 214. In one embodiment, the solid-state storage media 110a includes twenty-four solid-state storage elements 216a-216m per bank 214 with eight banks 214. In addition to the n×m storage elements 216a-216m, 218a-218m, 220a-220m, one or more additional columns (P) may also be addressed and operated in parallel with other solid-state storage elements 216a, 216b, 216m for one or more rows. The added P columns in one embodiment, store parity data for the portions of an ECC chunk (i.e., an ECC codeword) that span m storage elements for a particular bank. In one embodiment, each solid-state storage element 216, 218, 220 is comprised of single-level cell (“SLC”) devices. In another embodiment, each solid-state storage element 216, 218, 220 is comprised of multi-level cell (“MLC”) devices.
In one embodiment, solid-state storage elements that share a common line 211 on the storage I/O bus 210a (e.g., 216b, 218b, 220b) are packaged together. In one embodiment, a solid-state storage element 216, 218, 220 may have one or more dies per package with one or more packages stacked vertically and each die may be accessed independently. In another embodiment, a solid-state storage element (e.g., SSS 0.0 216a) may have one or more virtual dies per die and one or more dies per package and one or more packages stacked vertically and each virtual die may be accessed independently. In another embodiment, a solid-state storage element SSS 0.0 216a may have one or more virtual dies per die and one or more dies per package with some or all of the one or more dies stacked vertically and each virtual die may be accessed independently.
In one embodiment, two dies are stacked vertically with four stacks per group to form eight storage elements (e.g., SSS 0.0-SSS 8.0) 216a, 218a . . . 220a, each in a separate bank 214a, 214b . . . 214n. In another embodiment, 24 storage elements (e.g., SSS 0.0-SSS 0.24) 216a, 216b, . . . 216m form a logical bank 214a so that each of the eight logical banks has 24 storage elements (e.g., SSS0.0-SSS 8.24) 216, 218, 220. Data is sent to the solid-state storage media 110 over the storage I/O bus 210 to all storage elements of a particular group of storage elements (SSS 0.0-SSS 8.0) 216a, 218a, 220a. The storage control bus 212a is used to select a particular bank (e.g., Bank 0 214a) so that the data received over the storage I/O bus 210 connected to all banks 214 is written just to the selected bank 214a. 
In one embodiment, the storage I/O bus 210 is comprised of one or more independent I/O buses (“IIOBa-m” comprising 210a.a-m . . . 210n.a-m) wherein the solid-state storage elements within each column share one of the independent I/O buses that are connected to each solid-state storage element 216, 218, 220 in parallel. For example, one independent I/O bus 210a.a of the storage I/O bus 210a may be physically connected to a first solid-state storage element 216a, 218a, 220a of each bank 214a-n. A second independent I/O bus 210a.b of the storage I/O bus 210b may be physically connected to a second solid-state storage element 216b, 218b, 220b of each bank 214a-n. Each solid-state storage element 216a, 216b, 216m in a bank 214a (a row of solid-state storage elements as illustrated in FIG. 2) may be accessed simultaneously and/or in parallel. In one embodiment, where solid-state storage elements 216, 218, 220 comprise stacked packages of dies, all packages in a particular stack are physically connected to the same independent I/O bus. As used herein, “simultaneously” also includes near simultaneous access where devices are accessed at slightly different intervals to avoid switching noise. Simultaneously is used in this context to be distinguished from a sequential or serial access wherein commands and/or data are sent individually one after the other.
The banks 214a-n can be independently selected using the storage control bus 212. In one embodiment, a bank 214 is selected using a chip enable or chip select. Where both chip select and chip enable are available, the storage control bus 212 may select one package within a stack of packages. In other embodiments, other commands are used by the storage control bus 212 to individually select one package within a stack of packages. Solid-state storage elements 216, 218, 220 may also be selected through a combination of control signals and address information transmitted on storage I/O bus 210 and the storage control bus 212.
In one embodiment, each solid-state storage element 216, 218, 220 is partitioned into erase blocks and each erase block is partitioned into pages. An erase block on a solid-state storage element 216, 218 220 may be called a physical erase block or “PEB.” A page can be 2048 bytes (“2 kB”). In one example, a solid-state storage element (e.g., SSS 0.0) includes two registers and can program two pages so that a two-register solid-state storage element 216, 218, 220 has a capacity of 4 kB. A bank 214 of 20 solid-state storage elements 216a, 216b, 216m would then have an 80 kB capacity of pages accessed with the same address going out the independent I/O buses of the storage I/O bus 210.
This group of pages in a bank 214 of solid-state storage elements 216a, 216b, . . . 216m of 80 kB may be called a logical page or virtual page. Similarly, an erase block of each storage element 216a, 216b, . . . 216m of a bank 214a may be grouped to form a logical erase block (which may also be called a virtual erase block). In one embodiment, an erase block of pages within a solid-state storage element is erased when an erase command is received within the solid-state storage element. Whereas the size and number of erase blocks, pages, planes, or other logical and physical divisions within a solid-state storage element 216, 218, 220 are expected to change over time with advancements in technology, it is to be expected that many embodiments consistent with new configurations are possible and are consistent with the general description herein.
In one embodiment, when a packet is written to a particular location within a solid-state storage element 216, wherein the packet is intended to be written to a location within a particular page which is specific to a particular physical erase block of a particular storage element of a particular bank, a physical address is sent on the storage I/O bus 210 and is followed by the packet. The physical address contains enough information for the solid-state storage element 216 to direct the packet to the designated location within the page. Since all storage elements in a column of storage elements (e.g., SSS 0.0-SSS N.0 216a, 218a, . . . 220a) are connected to the same independent I/O bus (e.g., 210.a.a) of the storage I/O bus 210a, to reach the proper page and to avoid writing the data packet to similarly addressed pages in the column of storage elements (SSS 0.0-SSS N.0 216a, 218a, . . . 220a), the bank 214a that includes the solid-state storage element SSS 0.0 216a with the correct page where the data packet is to be written is selected by the storage control bus 212a and other banks 214b . . . 214n of the solid-state storage 110a are deselected.
Similarly, satisfying a read command on the storage I/O bus 210 requires a signal on the storage control bus 212 to select a single bank 214a and the appropriate page within that bank 214a. In one embodiment, a read command reads an entire page, and because there are multiple solid-state storage elements 216a, 216b, . . . 216m in parallel in a bank 214a, an entire logical page is read with a read command. However, the read command may be broken into subcommands, as will be explained below with respect to bank interleave. Similarly, an entire logical page may be written to the solid-state storage elements 216a, 216b, . . . 216m of a bank 214a in a write operation.
An erase block erase command may be sent out to erase an erase block over the storage I/O bus 210 with a particular erase block address to erase a particular erase block. In certain embodiments, storage controller 104a may send an erase block erase command over the parallel paths (independent I/O buses 210a-n.a-m) of the storage I/O bus 210 to erase a logical erase block, each with a particular erase block address to erase a particular erase block. Simultaneously, a particular bank (e.g., Bank 0 214a) is selected over the storage control bus 212 to prevent erasure of similarly addressed erase blocks in non-selected banks (e.g., Banks 1-N 214b-n). Alternatively, no particular bank (e.g., Bank 0 214a) is selected over the storage control bus 212 (or all of the banks are selected) to enable erasure of similarly addressed erase blocks in all of the banks (Banks 1-N 214b-n) in parallel. Other commands may also be sent to a particular location using a combination of the storage I/O bus 210 and the storage control bus 212. In additional embodiments, other ways to select a particular storage location using the bi-directional storage I/O bus 210 and the storage control bus 212 can be used.
In one embodiment, packets are written sequentially to the solid-state storage media 110. For example, storage controller 104a streams packets to storage write buffers of a bank 214a of storage elements 216 and, when the buffers are full, the packets are programmed to a designated logical page. Storage controller 104a then refills the storage write buffers with packets and, when full, the packets are written to the next logical page. The next logical page may be in the same bank 214a or another bank (e.g., 214b). This process continues, logical page after logical page, until a logical erase block is filled or the like. In another embodiment, the streaming may continue across logical erase block boundaries with the process continuing, logical erase block after logical erase block.
In a read, modify, write operation, data packets associated with requested data are located and read in a read operation. Data segments of the modified requested data that have been modified are not written to the location from which they are read. Instead, the modified data segments are again converted to data packets and then written sequentially to the next available location in the logical page currently being written. The index entries for the respective data packets are modified to point to the packets that contain the modified data segments. The entry or entries in the index for data packets associated with the same requested data that have not been modified will include pointers to original location of the unmodified data packets. Thus, if the original requested data is maintained, for example to maintain a previous version of the requested data, the original requested data will have pointers in the index to all data packets as originally written. The new requested data will have pointers in the index to some of the original data packets and pointers to the modified data packets in the logical page that is currently being written.
In a copy operation, the index includes an entry for the original requested data mapped to a number of packets stored in the solid-state storage media 110. When a copy is made, a new copy of the requested data is created and a new entry is created in the index mapping the new copy of the requested data to the original packets. The new copy of the requested data is also written to the solid-state storage media 110 with its location mapped to the new entry in the index. The new copy of the requested data packets may be used to identify the packets within the original requested data that are referenced in case changes have been made in the original requested data that have not been propagated to the copy of the requested data and the index is lost or corrupted.
Sequentially writing packets facilitates a more even use of the solid-state storage media 110 and allows the solid-storage device controller 202 to monitor storage hot spots and level usage of the various logical pages in the solid-state storage media 110. Sequentially writing packets also facilitates a powerful, efficient garbage collection system, which is described in detail below.
In various embodiments, the solid-state storage device controller 202 may also include a data bus 204, a local bus 206, a buffer controller 208, buffers 0-N 222a-n, a master controller 224, a direct memory access (“DMA”) controller 226, a memory controller 228, a dynamic memory array 230, a static random memory array 232, a management controller 234, a management bus 236, a bridge 238 to a system bus 240, and miscellaneous logic 242, which are described below. In other embodiments, the system bus 240 is coupled to one or more network interface cards (“NICs”) 244, some of which may include remote DMA (“RDMA”) controllers 246, one or more central processing unit (“CPU”) 248, one or more external memory controllers 250 and associated external memory arrays 252, one or more storage controllers 254, peer controllers 256, and application specific processors 258, which are described below. The components 244-258 connected to the system bus 240 may be located in the host computing system 114 or may be other devices.
The solid-state storage controller(s) 104 may communicate data to the solid-state storage media 110 over a storage I/O bus 210. In one embodiment where the solid-state storage is arranged in banks 214 and each bank 214 includes multiple storage elements 216a, 216b, 216m accessed in parallel, the storage I/O bus 210 is an array of busses, one for each column of storage elements 216, 218, 220 spanning the banks 214. As used herein, the term “storage I/O bus” may refer to one storage I/O bus 210 or an array of independent data busses wherein individual data busses of the array independently communicate different data relative to one another. In one embodiment, each storage I/O bus 210 accessing a column of storage elements (e.g., 216a, 218a, 220a) may include a logical-to-physical mapping for storage divisions (e.g., erase blocks) accessed in a column of storage elements 216a, 218a, 220a. This mapping (or bad block remapping) allows a logical address mapped to a physical address of a storage division to be remapped to a different storage division if the first storage division fails, partially fails, is inaccessible, or has some other problem.
Data may also be communicated to the solid-state storage controller(s) 104 from a requesting device, such as the host computing system 114, a network client, or the like through the system bus 240, bridge 238, local bus 206, buffer(s) 222, and finally over a data bus 204. The data bus 204 may be connected to one or more buffers 222a-n controlled with a buffer controller 208. The buffer controller 208, in one embodiment, controls transfer of data from the local bus 206 to the buffers 222 and through the data bus 204 to the pipeline input buffer 306 and output buffer 330. The buffer controller 208 may control how data arriving from a requesting device can be temporarily stored in a buffer 222 and then transferred onto a data bus 204, or vice versa, to account for different clock domains, to prevent data collisions, etc. The buffer controller 208 may work in conjunction with the master controller 224 to coordinate data flow. As data arrives, the data will arrive on the system bus 240, be transferred to the local bus 206 through a bridge 238.
The data, in certain embodiments, is transferred from the local bus 206 to one or more data buffers 222 as directed by the master controller 224 and the buffer controller 208. The data then flows out of the buffer(s) 222 to the data bus 204, through a solid-state controller 104, and on to the solid-state storage media 110 such as NAND flash or other storage media. In one embodiment, data and associated out-of-band metadata (“metadata”) arriving with the data is communicated using one or more data channels comprising one or more solid-state storage controllers 104a-104n-1 and associated solid-state storage media 110a-110n-1 while at least one channel (solid-state storage controller 104n, solid-state storage media 110n) is dedicated to in-band metadata, such as index information and other metadata generated internally to the solid-state storage device 102.
The local bus 206 may comprise a bidirectional bus or set of busses that allows for communication of data and commands between devices internal to the solid-state storage device controller 202 and between devices internal to the solid-state storage device 102 and devices 244-258 connected to the system bus 240. The bridge 238 facilitates communication between the local bus 206 and system bus 240. Other embodiments are possible, such as ring structures or switched star configurations and functions of buses 240, 206, 204, 210 and bridges 238.
The system bus 240 may comprise a bus of a host computing system 114 or other device in which the solid-state storage device 102 is installed or connected. In one embodiment, the system bus 240 may be a PCI-e bus, a Serial Advanced Technology Attachment (“serial ATA”) bus, parallel ATA, or the like. In another embodiment, the system bus 240 is an external bus such as small computer system interface (“SCSI”), FireWire, Fiber Channel, USB, PCIe-AS, or the like. The solid-state storage device 102 may be packaged to fit internally to a device or as an externally connected device.
The solid-state storage device controller 202 includes a master controller 224 that controls higher-level functions within the solid-state storage device 102. The master controller 224, in various embodiments, controls data flow by interpreting object requests and other requests, directs creation of indexes to map object identifiers associated with data to physical locations of associated data, coordinating DMA requests, etc. Many of the functions described herein are controlled wholly or in part by the master controller 224.
In one embodiment, the master controller 224 uses embedded controller(s). In another embodiment, the master controller 224 uses local memory such as a dynamic memory array 230 (dynamic random access memory “DRAM”), a static memory array 232 (static random access memory “SRAM”), etc. In one embodiment, the local memory is controlled using the master controller 224. In another embodiment, the master controller 224 accesses the local memory via a memory controller 228. In another embodiment, the master controller 224 runs a Linux server and may support various common server interfaces, such as the World Wide Web, hyper-text markup language (“HTML”), etc. In another embodiment, the master controller 224 uses a nano-processor. The master controller 224 may be constructed using programmable or standard logic, or any combination of controller types listed above. In light of this disclosure, many embodiments for the master controller 224 are possible.
In one embodiment, where the storage device/solid-state storage device controller 202 manages multiple data storage devices/solid-state storage media 110a-n, the master controller 224 divides the work load among internal controllers, such as the solid-state storage controllers 104a-n. For example, the master controller 224 may divide an object to be written to the data storage devices (e.g., solid-state storage media 110a-n) so that a portion of the object is stored on each of the attached data storage devices. This feature is a performance enhancement allowing quicker storage and access to an object. In one embodiment, the master controller 224 is implemented using an FPGA. In another embodiment, the firmware within the master controller 224 may be updated through the management bus 236, the system bus 240 over a network connected to a NIC 244 or other device connected to the system bus 240.
In one embodiment, the master controller 224, which manages objects, emulates block storage such that a host computing system 114 or other device connected to the storage device/solid-state storage device 102 views the storage device/solid-state storage device 102 as a block storage device and sends data to specific physical addresses in the storage device/solid-state storage device 102. The master controller 224 then divides up the blocks and stores the data blocks as it would objects. The master controller 224 then maps the blocks and physical address sent with the block to the actual locations determined by the master controller 224. The mapping is stored in the object index. For block emulation, a block device application program interface (“API”) may be provided in a driver in a computer such as the host computing system 114, or other device wishing to use the storage device/solid-state storage device 102 as a block storage device.
In another embodiment, the master controller 224 coordinates with NIC controllers 244 and embedded RDMA controllers 246 to deliver just-in-time RDMA transfers of data and command sets. NIC controller 244 may be hidden behind a non-transparent port to enable the use of custom drivers. Also, a driver on a host computing system 114 may have access to the computer network 116 through an I/O memory driver using a standard stack API and operating in conjunction with NICs 244.
In one embodiment, the master controller 224 is also a redundant array of independent drive (“RAID”) controller. Where the data storage device/solid-state storage device 102 is networked with one or more other data storage devices/solid-state storage devices 102, the master controller 224 may be a RAID controller for single tier RAID, multi-tier RAID, progressive RAID, etc. The master controller 224 also allows some objects to be stored in a RAID array and other objects to be stored without RAID. In another embodiment, the master controller 224 may be a distributed RAID controller element. In another embodiment, the master controller 224 may comprise many RAID, distributed RAID, and other functions as described elsewhere. In one embodiment, the master controller 224 controls storage of data in a RAID-like structure where parity information is stored in one or more storage elements 216, 218, 220 of a logical page where the parity information protects data stored in the other storage elements 216, 218, 220 of the same logical page.
In one embodiment, the master controller 224 coordinates with single or redundant network managers (e.g., switches) to establish routing, to balance bandwidth utilization, failover, etc. In another embodiment, the master controller 224 coordinates with integrated application specific logic (via local bus 206) and associated driver software. In another embodiment, the master controller 224 coordinates with attached application specific processors 258 or logic (via the external system bus 240) and associated driver software. In another embodiment, the master controller 224 coordinates with remote application specific logic (via the computer network 116) and associated driver software. In another embodiment, the master controller 224 coordinates with the local bus 206 or external bus attached hard disk drive (“HDD”) storage controller.
In one embodiment, the master controller 224 communicates with one or more storage controllers 254 where the storage device/solid-state storage device 102 may appear as a storage device connected through a SCSI bus, Internet SCSI (“iSCSI”), fiber channel, etc. Meanwhile the storage device/solid-state storage device 102 may autonomously manage objects and may appear as an object file system or distributed object file system. The master controller 224 may also be accessed by peer controllers 256 and/or application specific processors 258.
In another embodiment, the master controller 224 coordinates with an autonomous integrated management controller to periodically validate FPGA code and/or controller software, validate FPGA code while running (reset) and/or validate controller software during power on (reset), support external reset requests, support reset requests due to watchdog timeouts, and support voltage, current, power, temperature, and other environmental measurements and setting of threshold interrupts. In another embodiment, the master controller 224 manages garbage collection to free erase blocks for reuse. In another embodiment, the master controller 224 manages wear leveling. In another embodiment, the master controller 224 allows the data storage device/solid-state storage device 102 to be partitioned into multiple logical devices and allows partition-based media encryption. In yet another embodiment, the master controller 224 supports a solid-state storage controller 104 with advanced, multi-bit ECC correction. In light of this disclosure, other features and functions of a master controller 224 in a storage controller 202, or more specifically in a solid-state storage device 102 are possible.
In one embodiment, the solid-state storage device controller 202 includes a memory controller 228, which controls a dynamic random memory array 230 and/or a static random memory array 232. As stated above, the memory controller 228 may be independent or integrated with the master controller 224. The memory controller 228 may control volatile memory of some type, such as DRAM (dynamic random memory array 230) and SRAM (static random memory array 232). In other examples, the memory controller 228 also controls other memory types such as electrically erasable programmable read only memory (“EEPROM”), etc. In other embodiments, the memory controller 228 controls two or more memory types and the memory controller 228 may include more than one controller. In certain embodiments, the memory controller 228 controls as much SRAM 232 as is feasible and by DRAM 230 to supplement the SRAM 232.
In one embodiment, the object index is stored in memory 230, 232 and then periodically off-loaded to a channel of the solid-state storage media 110n or other non-volatile memory. In light of this disclosure, other uses and configurations of the memory controller 228, dynamic memory array 230, and static memory array 232 are possible.
In one embodiment, the solid-state storage device controller 202 includes a DMA controller 226 that controls DMA operations between the storage device/solid-state storage device 102 and one or more external memory controllers 250 and associated external memory arrays 252 and CPUs 248. Note that the external memory controllers 250 and external memory arrays 252 are called external because they are external to the storage device/solid-state storage device 102. In addition, the DMA controller 226 may also control RDMA operations with requesting devices through a NIC 244 and associated RDMA controller 246.
In one embodiment, the solid-state storage device controller 202 includes a management controller 234 connected to a management bus 236. The management controller 234 may manage environmental metrics and status of the storage device/solid-state storage device 102. The management controller 234 may monitor device temperature, fan speed, power supply settings, etc. over the management bus 236. The management controller 234 may support the reading and programming of erasable programmable read only memory (“EEPROM”) for storage of FPGA code and controller software. The management bus 236 may be connected to the various components within the storage device/solid-state storage device 102. The management controller 234 may communicate alerts, interrupts, etc. over the local bus 206 or may include a separate connection to a system bus 240 or other bus. In one embodiment, the management bus 236 is an Inter-Integrated Circuit (“I2C”) bus. In light of this disclosure, other related functions and uses of a management controller 234 connected to components of the storage device/solid-state storage device 102 by a management bus 236 are possible.
In one embodiment, the solid-state storage device controller 202 includes miscellaneous logic 242 that may be customized for a specific application. In embodiments where the solid-state device controller 202 or master controller 224 is/are configured using a FPGA or other configurable controller, custom logic may be included based on a particular application, customer requirement, storage requirement, etc.
FIG. 3 is a schematic block diagram illustrating one embodiment 300 of a solid-state storage controller 104 with a write data pipeline 106 and a read data pipeline 108 in a solid-state storage device 102. The embodiment 300 includes a data bus 204, a local bus 206, and buffer control 208, which are substantially similar to those described in relation to the solid-state storage device controller 202 of FIG. 2. The write data pipeline 106 includes a packetizer 302 and an error-correcting code (“ECC”) generator 304. In other embodiments, the write data pipeline 106 includes an input buffer 306, a write synchronization buffer 308, a write program module 310, a compression module 312, an encryption module 314, a garbage collector bypass 316 (with a portion within the read data pipeline 108), a media encryption module 318, and a write buffer 320. The read data pipeline 108 includes a read synchronization buffer 328, an ECC correction module 322, a depacketizer 324, an alignment module 326, and an output buffer 330. In other embodiments, the read data pipeline 108 may include a media decryption module 332, a portion of the garbage collector bypass 316, a decryption module 334, a decompression module 336, and a read program module 338. The solid-state storage controller 104 may also include control and status registers 340 and control queues 342, a bank interleave controller 344, a synchronization buffer 346, a storage bus controller 348, and a multiplexer (“MUX”) 350. The components of the solid-state controller 104 and associated write data pipeline 106 and read data pipeline 108 are described below. In other embodiments, synchronous solid-state storage media 110 may be used and synchronization buffers 308 328 may be eliminated.
The write data pipeline 106 includes a packetizer 302 that receives a data or metadata segment to be written to the solid-state storage, either directly or indirectly through another write data pipeline 106 stage, and creates one or more packets sized for the solid-state storage media 110. The data or metadata segment may be part of a data structure such as an object, but may also include an entire data structure. In another embodiment, the data segment is part of a block of data, but may also include an entire block of data. A set of data such as a data structure may be received from a computer such as the host computing system 114, or other computer or device and is transmitted to the solid-state storage device 102 in data segments streamed to the solid-state storage device 102. A data segment may also be known by another name, such as data parcel, but as referenced herein includes all or a portion of a data structure or data block.
Each data structure is stored as one or more packets. Each data structure may have one or more container packets. Each packet contains a header. The header may include a header type field. Type fields may include data, attribute, metadata, data segment delimiters (multi-packet), data structures, data linkages, and the like. The header may also include information regarding the size of the packet, such as the number of bytes of data included in the packet. The length of the packet may be established by the packet type. The header may include information that establishes the relationship of the packet to a data structure. An example might be the use of an offset in a data packet header to identify the location of the data segment within the data structure. In certain embodiments, other information may be included in a header added to data by a packetizer 302 and other information may be added to a data packet.
Each packet includes a header and possibly data from the data or metadata segment. The header of each packet includes pertinent information to relate the packet to the data structure to which the packet belongs. For example, the header may include an object identifier or other data structure identifier and offset that indicate the data segment, object, data structure or data block from which the data packet was formed. The header may also include a logical address used by the storage bus controller 348 to store the packet. The header may also include information regarding the size of the packet, such as the number of bytes included in the packet. The header may also include a sequence number that identifies where the data segment belongs with respect to other packets within the data structure when reconstructing the data segment or data structure. The header may include a header type field. Type fields may include data, data structure attributes, metadata, data segment delimiters (multi-packet), data structure types, data structure linkages, and the like. In certain embodiments, other information may be included in a header added to data or metadata by a packetizer 302 and other information may be added to a packet.
The write data pipeline 106 includes an ECC generator 304 that that generates one or more error-correcting codes (“ECC”) for the one or more packets received from the packetizer 302. The ECC generator 304, in certain embodiments, uses an error-correcting algorithm to generate ECC check bits, which are stored with the one or more data packets. The ECC codes generated by the ECC generator 304 together with the one or more data packets associated with the ECC codes comprise an ECC chunk. The ECC data stored with the one or more data packets is used to detect and to correct errors introduced into the data through transmission and storage. In one embodiment, packets are streamed into the ECC generator 304 as un-encoded blocks of length N. A syndrome of length S is calculated, appended, and output as an encoded block of length N+S. The value of N and S are dependent upon the characteristics of the ECC algorithm, which is selected to achieve specific performance, efficiency, and robustness metrics. In one embodiment, there is no fixed relationship between the ECC blocks and the packets; the packet may comprise more than one ECC block; the ECC block may comprise more than one packet; and a first packet may end anywhere within the ECC block and a second packet may begin after the end of the first packet within the same ECC block. In one embodiment, ECC algorithms are not dynamically modified. In one embodiment, the ECC data stored with the data packets is robust enough to correct errors in more than two bits.
Beneficially, using a robust ECC algorithm allowing more than single bit correction or even double bit correction allows the life of the solid-state storage media 110 to be extended. For example, if flash memory is used as the storage medium in the solid-state storage media 110, the flash memory may be written approximately 100,000 times without error per erase cycle. This usage limit may be extended using a robust ECC algorithm. Having the ECC generator 304 and corresponding ECC correction module 322 onboard the solid-state storage device 102, the solid-state storage device 102 can internally correct errors and has a longer useful life than if a less robust ECC algorithm is used, such as single bit correction. However, in other embodiments the ECC generator 304 may use a less robust algorithm and may correct single-bit or double-bit errors. In another embodiment, the solid-state storage device 110 may comprise less reliable storage such as multi-level cell (“MLC”) flash in order to increase capacity, which storage may not be sufficiently reliable without more robust ECC algorithms.
In one embodiment, the write pipeline 106 includes an input buffer 306 that receives a data segment to be written to the solid-state storage media 110 and stores the incoming data segments until the next stage of the write data pipeline 106, such as the packetizer 302 (or other stage for a more complex write data pipeline 106) is ready to process the next data segment. The input buffer 306 may allow for discrepancies between the rate data segments are received and processed by the write data pipeline 106 using an appropriately sized data buffer. The input buffer 306 also allows the data bus 204 to transfer data to the write data pipeline 106 at rates greater than can be sustained by the write data pipeline 106 in order to improve efficiency of operation of the data bus 204. When the write data pipeline 106 does not include an input buffer 306, a buffering function may be performed elsewhere, such as in the solid-state storage device 102 but outside the write data pipeline 106, in the host computing system 114, such as within a network interface card (“NIC”), or at another device, for example when using remote direct memory access (“RDMA”).
In another embodiment, the write data pipeline 106 also includes a write synchronization buffer 308 that buffers packets received from the ECC generator 304 prior to writing the packets to the solid-state storage media 110. The write synchronization buffer 308 is located at a boundary between a local clock domain and a solid-state storage clock domain and provides buffering to account for the clock domain differences. In other embodiments, synchronous solid-state storage media 110 may be used and synchronization buffers 308 328 may be eliminated.
In one embodiment, the write data pipeline 106 also includes a media encryption module 318 that receives the one or more packets from the packetizer 302, either directly or indirectly, and encrypts the one or more packets using an encryption key unique to the solid-state storage device 102 prior to sending the packets to the ECC generator 304. The entire packet may be encrypted, including the headers. In another embodiment, headers are not encrypted. In this disclosure, encryption key is understood to mean a secret encryption key that is managed externally from a solid-state storage controller 104.
The media encryption module 318 and corresponding media decryption module 332 provide a level of security for data stored in the solid-state storage media 110. For example, where data is encrypted with the media encryption module 318, if the solid-state storage media 110 is connected to a different solid-state storage controller 104, solid-state storage device 102, or server, the contents of the solid-state storage media 110 may not be read without use of the same encryption key used during the write of the data to the solid-state storage media 110 without significant effort.
In one embodiment, the solid-state storage device 102 does not store the encryption key in non-volatile storage and allows no external access to the encryption key. The encryption key is provided to the solid-state storage controller 104 during initialization. The solid-state storage device 102 may use and store a non-secret cryptographic nonce that is used in conjunction with an encryption key. A different nonce may be stored with every packet. Data segments may be split between multiple packets with unique nonces for the purpose of improving protection by the encryption algorithm.
The encryption key may be received from a host computing system 114, a server, key manager, or other device that manages the encryption key to be used by the solid-state storage controller 104. In another embodiment, the solid-state storage media 110 may have two or more partitions and the solid-state storage controller 104 behaves as though it was two or more solid-state storage controllers 104, each operating on a single partition within the solid-state storage media 110. In this embodiment, a unique media encryption key may be used with each partition.
In another embodiment, the write data pipeline 106 also includes an encryption module 314 that encrypts a data or metadata segment received from the input buffer 306, either directly or indirectly, prior sending the data segment to the packetizer 302, the data segment encrypted using an encryption key received in conjunction with the data segment. The encryption keys used by the encryption module 314 to encrypt data may not be common to all data stored within the solid-state storage device 102 but may vary on an per data structure basis and received in conjunction with receiving data segments as described below. For example, an encryption key for a data segment to be encrypted by the encryption module 314 may be received with the data segment or may be received as part of a command to write a data structure to which the data segment belongs. The solid-state storage device 102 may use and store a non-secret cryptographic nonce in each data structure packet that is used in conjunction with the encryption key. A different nonce may be stored with every packet. Data segments may be split between multiple packets with unique nonces for the purpose of improving protection by the encryption algorithm.
The encryption key may be received from a host computing system 114, another computer, key manager, or other device that holds the encryption key to be used to encrypt the data segment. In one embodiment, encryption keys are transferred to the solid-state storage controller 104 from one of a solid-state storage device 102, host computing system 114, computer, or other external agent, which has the ability to execute industry standard methods to securely transfer and protect private and public keys.
In one embodiment, the encryption module 314 encrypts a first packet with a first encryption key received in conjunction with the packet and encrypts a second packet with a second encryption key received in conjunction with the second packet. In another embodiment, the encryption module 314 encrypts a first packet with a first encryption key received in conjunction with the packet and passes a second data packet on to the next stage without encryption. Beneficially, the encryption module 314 included in the write data pipeline 106 of the solid-state storage device 102 allows data structure-by-data structure or segment-by-segment data encryption without a single file system or other external system to keep track of the different encryption keys used to store corresponding data structures or data segments. Each requesting device or related key manager independently manages encryption keys used to encrypt only the data structures or data segments sent by the requesting device.
In one embodiment, the encryption module 314 may encrypt the one or more packets using an encryption key unique to the solid-state storage device 102. The encryption module 314 may perform this media encryption independently, or in addition to the encryption described above. The entire packet may be encrypted, including the headers. In another embodiment, headers are not encrypted. The media encryption by the encryption module 314 provides a level of security for data stored in the solid-state storage media 110. For example, where data is encrypted with media encryption unique to the specific solid-state storage device 102, if the solid-state storage media 110 is connected to a different solid-state storage controller 104, solid-state storage device 102, or host computing system 114, the contents of the solid-state storage media 110 may not be read without use of the same encryption key used during the write of the data to the solid-state storage media 110 without significant effort.
In another embodiment, the write data pipeline 106 includes a compression module 312 that compresses the data for metadata segment prior to sending the data segment to the packetizer 302. The compression module 312 may compress a data or metadata segment using a compression routine to reduce the storage size of the segment. For example, if a data segment includes a string of 512 zeros, the compression module 312 may replace the 512 zeros with code or token indicating the 512 zeros where the code is much more compact than the space taken by the 512 zeros.
In one embodiment, the compression module 312 compresses a first segment with a first compression routine and passes along a second segment without compression. In another embodiment, the compression module 312 compresses a first segment with a first compression routine and compresses the second segment with a second compression routine. Having this flexibility within the solid-state storage device 102 is beneficial so that computing systems 114 or other devices writing data to the solid-state storage device 102 may each specify a compression routine or so that one can specify a compression routine while another specifies no compression. Selection of compression routines may also be selected according to default settings on a per data structure type or data structure class basis. For example, a first data structure of a specific data structure may be able to override default compression routine settings and a second data structure of the same data structure class and data structure type may use the default compression routine and a third data structure of the same data structure class and data structure type may use no compression.
In one embodiment, the write data pipeline 106 includes a garbage collector bypass 316 that receives data segments from the read data pipeline 108 as part of a data bypass in a garbage collection system. A garbage collection system may mark packets that are no longer valid, because the packet is marked for deletion, has been modified and the modified data is stored in a different location, or the like. At some point, the garbage collection system determines that a particular section (e.g., an erase block) of storage may be recovered. This determination may be due to a lack of available storage capacity, the percentage of data marked as invalid reaching a threshold, a consolidation of valid data, an error detection rate for that section of storage reaching a threshold, or improving performance based on data distribution, etc. Numerous factors may be considered by a garbage collection algorithm to determine when a section of storage is to be recovered.
Once a section of storage has been marked for recovery, valid packets in the section may be relocated. The garbage collector bypass 316 allows packets to be read into the read data pipeline 108 and then transferred directly to the write data pipeline 106 without being routed out of the solid-state storage controller 104. In one embodiment, the garbage collector bypass 316 is part of an autonomous garbage collector system that operates within the solid-state storage device 102. This allows the solid-state storage device 102 to manage data so that data is systematically spread throughout the solid-state storage media 110 to improve performance, data reliability and to avoid overuse and underuse of any one location or area of the solid-state storage media 110 and to lengthen the useful life of the solid-state storage media 110.
The garbage collector bypass 316 coordinates insertion of segments into the write data pipeline 106 with other segments being written by computing systems 114 or other devices. In the depicted embodiment, the garbage collector bypass 316 is before the packetizer 302 in the write data pipeline 106 and after the depacketizer 324 in the read data pipeline 108, but may also be located elsewhere in the read and write data pipelines 106, 108. The garbage collector bypass 316 may be used during a flush of the write pipeline 108 to fill the remainder of the logical page in order to improve the efficiency of storage within the solid-state storage media 110 and thereby reduce the frequency of garbage collection.
In one embodiment, the write data pipeline 106 includes a write buffer 320 that buffers data for efficient write operations. The write buffer 320 may include enough capacity for packets to fill at least one logical page in the solid-state storage media 110. This allows a write operation to send an entire logical page of data to the solid-state storage media 110 without interruption. By sizing the write buffer 320 of the write data pipeline 106 and buffers within the read data pipeline 108 to be the same capacity or larger than a storage write buffer within the solid-state storage media 110, writing and reading data is more efficient since a single write command may be crafted to send a full logical page of data to the solid-state storage media 110 instead of multiple commands.
While the write buffer 320 is being filled, the solid-state storage media 110 may be used for other read operations. This is advantageous because other solid-state devices with a smaller write buffer or no write buffer may tie up the solid-state storage when data is written to a storage write buffer and data flowing into the storage write buffer stalls. Read operations will be blocked until the entire storage write buffer is filled and programmed. Another approach for systems without a write buffer or a small write buffer is to flush the storage write buffer that is not full in order to enable reads. Again, this is inefficient because multiple write/program cycles are required to fill a page.
For depicted embodiment with a write buffer 320 sized larger than a logical page, a single write command, which includes numerous subcommands, can then be followed by a single program command to transfer the page of data from the storage write buffer in each solid-state storage element 216, 218, 220 to the designated page within each solid-state storage element 216, 218, 220. This technique has the benefits of eliminating partial page programming, which is known to reduce data reliability and durability and freeing up the destination bank for reads and other commands while the buffer fills.
In one embodiment, the write buffer 320 is a ping-pong buffer where one side of the buffer is filled and then designated for transfer at an appropriate time while the other side of the ping-pong buffer is being filled. In another embodiment, the write buffer 320 includes a first-in first-out (“FIFO”) register with a capacity of more than a logical page of data segments. In further embodiments, other write buffer 320 configurations that allow a logical page of data to be stored prior to writing the data to the solid-state storage media 110 may be used.
In another embodiment, the write buffer 320 is sized smaller than a logical page so that less than a page of information could be written to a storage write buffer in the solid-state storage media 110. In the embodiment, to prevent a stall in the write data pipeline 106 from holding up read operations, data is queued using the garbage collection system that needs to be moved from one location to another as part of the garbage collection process. In case of a data stall in the write data pipeline 106, the data can be fed through the garbage collector bypass 316 to the write buffer 320 and then on to the storage write buffer in the solid-state storage media 110 to fill the pages of a logical page prior to programming the data. In this way, a data stall in the write data pipeline 106 would not stall reading from the solid-state storage device 102.
In another embodiment, the write data pipeline 106 includes a write program module 310 with one or more user-definable functions within the write data pipeline 106. The write program module 310 allows a user to customize the write data pipeline 106. A user may customize the write data pipeline 106 based on a particular data requirement or application. Where the solid-state storage controller 104 is an FPGA, the user may program the write data pipeline 106 with custom commands and functions relatively easily. A user may also use the write program module 310 to include custom functions with an ASIC, however, customizing an ASIC may be more difficult than with an FPGA. The write program module 310 may include buffers and bypass mechanisms to allow a first data segment to execute in the write program module 310 while a second data segment may continue through the write data pipeline 106. In another embodiment, the write program module 310 may include a processor core that can be programmed through software.
Note that the write program module 310 is shown between the input buffer 306 and the compression module 312, however, the write program module 310 could be anywhere in the write data pipeline 106 and may be distributed among the various stages 302-320. In addition, there may be multiple write program modules 310 distributed among the various states 302-320 that are programmed and operate independently. In addition, the order of the stages 302-320 may be altered. In light of this disclosure, other workable alterations to the order of the stages 302-320 based on particular user requirements may be used.
The read data pipeline 108 includes an ECC correction module 322 that determines if a data error exists in ECC blocks a requested packet received from the solid-state storage media 110 by using ECC stored with each ECC block of the requested packet. The ECC correction module 322 then corrects any errors in the requested packet if any error exists and the errors are correctable using the ECC. For example, if the ECC can detect an error in six bits but can only correct three bit errors, the ECC correction module 322 corrects ECC blocks of the requested packet with up to three bits in error. The ECC correction module 322 corrects the bits in error by changing the bits in error to the correct one or zero state so that the requested data packet is identical to when it was written to the solid-state storage media 110 and the ECC was generated for the packet.
If the ECC correction module 322 determines that the requested packets contains more bits in error than the ECC can correct, the ECC correction module 322 cannot correct the errors in the corrupted ECC blocks of the requested packet and sends an interrupt. In one embodiment, the ECC correction module 322 sends an interrupt with a message indicating that the requested packet is in error. The message may include information that the ECC correction module 322 cannot correct the errors or the inability of the ECC correction module 322 to correct the errors may be implied. In another embodiment, the ECC correction module 322 sends the corrupted ECC blocks of the requested packet with the interrupt and/or the message.
In one embodiment, a corrupted ECC block or portion of a corrupted ECC block of the requested packet that cannot be corrected by the ECC correction module 322 is read by the master controller 224, corrected, and returned to the ECC correction module 322 for further processing by the read data pipeline 108. In one embodiment, a corrupted ECC block or portion of a corrupted ECC block of the requested packet is sent to the device requesting the data. The requesting device may correct the ECC block or replace the data using another copy, such as a backup or mirror copy, and then may use the replacement data of the requested data packet or return it to the read data pipeline 108. The requesting device may use header information in the requested packet in error to identify data required to replace the corrupted requested packet or to replace the data structure to which the packet belongs. In another embodiment, the solid-state storage controller 104 stores data using some type of RAID and is able to recover the corrupted data. In another embodiment, the ECC correction module 322 sends an interrupt and/or message and the receiving device fails the read operation associated with the requested data packet. In further embodiments, other options and actions to be taken as a result of the ECC correction module 322 determining that one or more ECC blocks of the requested packet are corrupted and that the ECC correction module 322 cannot correct the errors.
The read data pipeline 108 includes a depacketizer 324 that receives ECC blocks of the requested packet from the ECC correction module 322, directly or indirectly, and checks and removes one or more packet headers. The depacketizer 324 may validate the packet headers by checking packet identifiers, data length, data location, etc. within the headers. In one embodiment, the header includes a hash code that can be used to validate that the packet delivered to the read data pipeline 108 is the requested packet. The depacketizer 324 also removes the headers from the requested packet added by the packetizer 302. The depacketizer 324 may directed to not operate on certain packets but pass these forward without modification. An example might be a container label that is requested during the course of a rebuild process where the header information is required for index reconstruction. Further examples include the transfer of packets of various types destined for use within the solid-state storage device 102. In another embodiment, the depacketizer 324 operation may be packet type dependent.
The read data pipeline 108 includes an alignment module 326 that receives data from the depacketizer 324 and removes unwanted data. In one embodiment, a read command sent to the solid-state storage media 110 retrieves a packet of data. A device requesting the data may not require all data within the retrieved packet and the alignment module 326 removes the unwanted data. If all data within a retrieved page is requested data, the alignment module 326 does not remove any data.
The alignment module 326 re-formats the data as data segments of a data structure in a form compatible with a device requesting the data segment prior to forwarding the data segment to the next stage. As data is processed by the read data pipeline 108, in certain embodiments, the size of data segments or packets may change at various stages. The alignment module 326 uses received data to format the data into data segments suitable to be sent to the requesting device and joined to form a response. For example, data from a portion of a first data packet may be combined with data from a portion of a second data packet. If a data segment is larger than a data requested by the requesting device, the alignment module 326 may discard the unwanted data.
In one embodiment, the read data pipeline 108 includes a read synchronization buffer 328 that buffers one or more requested packets read from the solid-state storage media 110 prior to processing by the read data pipeline 108. The read synchronization buffer 328 is at the boundary between the solid-state storage clock domain and the local bus clock domain and provides buffering to account for the clock domain differences.
In another embodiment, the read data pipeline 108 includes an output buffer 330 that receives requested packets from the alignment module 326 and stores the packets prior to transmission to the requesting device. The output buffer 330 accounts for differences between when data segments are received from stages of the read data pipeline 108 and when the data segments are transmitted to other parts of the solid-state storage controller 104 or to the requesting device. The output buffer 330 also allows the data bus 204 to receive data from the read data pipeline 108 at rates greater than can be sustained by the read data pipeline 108 in order to improve efficiency of operation of the data bus 204.
In one embodiment, the read data pipeline 108 includes a media decryption module 332 that receives one or more encrypted requested packets from the ECC correction module 322 and decrypts the one or more requested packets using the encryption key unique to the solid-state storage device 102 prior to sending the one or more requested packets to the depacketizer 324. In one embodiment, the encryption key used to decrypt data by the media decryption module 332 is identical to the encryption key used by the media encryption module 318. In another embodiment, the solid-state storage media 110 may have two or more partitions and the solid-state storage controller 104 behaves as though it was two or more solid-state storage controllers 104 each operating on a single partition within the solid-state storage media 110. In this embodiment, a unique media encryption key may be used with each partition.
In another embodiment, the read data pipeline 108 includes a decryption module 334 that decrypts a data segment formatted by the depacketizer 324 prior to sending the data segment to the output buffer 330. The data segment may be decrypted using an encryption key received in conjunction with the read request that initiates retrieval of the requested packet received by the read synchronization buffer 328. The decryption module 334 may decrypt a first packet with an encryption key received in conjunction with the read request for the first packet and then may decrypt a second packet with a different encryption key or may pass the second packet on to the next stage of the read data pipeline 108 without decryption. When the packet was stored with a non-secret cryptographic nonce, the nonce is used in conjunction with an encryption key to decrypt the data packet. The encryption key may be received from a host computing system 114, a client, key manager, or other device that manages the encryption key to be used by the solid-state storage controller 104.
In another embodiment, the read data pipeline 108 includes a decompression module 336 that decompresses a data segment formatted by the depacketizer 324. In one embodiment, the decompression module 336 uses compression information stored in one or both of the packet header and the container label to select a complementary routine to that used to compress the data by the compression module 312. In another embodiment, the decompression routine used by the decompression module 336 is dictated by the device requesting the data segment being decompressed. In another embodiment, the decompression module 336 selects a decompression routine according to default settings on a per data structure type or data structure class basis. A first packet of a first object may be able to override a default decompression routine and a second packet of a second data structure of the same data structure class and data structure type may use the default decompression routine and a third packet of a third data structure of the same data structure class and data structure type may use no decompression.
In another embodiment, the read data pipeline 108 includes a read program module 338 that includes one or more user-definable functions within the read data pipeline 108. The read program module 338 has similar characteristics to the write program module 310 and allows a user to provide custom functions to the read data pipeline 108. The read program module 338 may be located as shown in FIG. 3, may be located in another position within the read data pipeline 108, or may include multiple parts in multiple locations within the read data pipeline 108. Additionally, there may be multiple read program modules 338 within multiple locations within the read data pipeline 108 that operate independently. In certain embodiments, other forms of a read program module 338 within a read data pipeline 108 may be used. As with the write data pipeline 106, the stages of the read data pipeline 108 may be rearranged and other orders of stages within the read data pipeline 108 are possible.
The solid-state storage controller 104 includes control and status registers 340 and corresponding control queues 342. The control and status registers 340 and control queues 342 facilitate control and sequencing commands and subcommands associated with data processed in the write and read data pipelines 106, 108. For example, a data segment in the packetizer 302 may have one or more corresponding control commands or instructions in a control queue 342 associated with the ECC generator 304. As the data segment is packetized, some of the instructions or commands may be executed within the packetizer 302. Other commands or instructions may be passed to the next control queue 342 through the control and status registers 340 as the newly formed data packet created from the data segment is passed to the next stage.
Commands or instructions may be simultaneously loaded into the control queues 342 for a packet being forwarded to the write data pipeline 106 with each pipeline stage pulling the appropriate command or instruction as the respective packet is executed by that stage. Similarly, commands or instructions may be simultaneously loaded into the control queues 342 for a packet being requested from the read data pipeline 108 with each pipeline stage pulling the appropriate command or instruction as the respective packet is executed by that stage. In further embodiments, other features and functions of control and status registers 340 and control queues 342 are possible.
The solid-state storage controller 104 and/or solid-state storage device 102 may also include a bank interleave controller 344, a synchronization buffer 346, a storage bus controller 348, and a multiplexer (“MUX”) 350, which are described in relation to FIG. 4A.
FIG. 4A is a schematic block diagram illustrating one embodiment 400 of a bank interleave controller 344 in the solid-state storage controller 104. The bank interleave controller 344 is connected to the control and status registers 340 and to the storage I/O bus 210 and storage control bus 212 through the MUX 350, storage bus controller 348, and synchronization buffer 346, which are described below. The bank interleave controller 344 includes a read agent 402, a write agent 404, an erase agent 406, a management agent 408, read queues 410a-n, write queues 412a-n, erase queues 414a-n, and management queues 416a-n for the banks 214 in the solid-state storage media 110, bank controllers 418a-n, a bus arbiter 420, and a status MUX 422, which are described below. The storage bus controller 348 includes a mapping module 424 with a remapping module 430, a status capture module 426, and a NAND bus controller 428, which are described below.
The bank interleave controller 344 directs one or more commands to two or more queues in the bank interleave controller 304 and coordinates among the banks 214 of the solid-state storage media 110 execution of the commands stored in the queues, such that a command of a first type executes on one bank 214a while a command of a second type executes on a second bank 214b. In one embodiment, the one or more commands may be separated by command type into the queues. Each bank 214 of the solid-state storage media 110 has a corresponding set of queues within the bank interleave controller 344 and each set of queues includes a queue for each command type.
The bank interleave controller 344 coordinates among the banks 214 of the solid-state storage media 110 execution of the commands stored in the queues. For example, a command of a first type executes on one bank 214a while a command of a second type executes on a second bank 214b. The command types and queue types, in one embodiment, may include read commands, discard/TRIM commands, and write commands and queues 410, 412 (e.g., I/O operations), but may also include other commands and queues that are storage media specific. For example, in the embodiment depicted in FIG. 4A, erase and management queues 414, 416 are included and would be appropriate for flash memory, NRAM, MRAM, DRAM, PRAM, etc. In other words, while an erase command is a type of storage device management operation, the interleave controller 344 may include a separate erase queue 414 for such commands. In other embodiments, discard/TRIM, erase, and other similar commands are other examples of storage device management operations. In certain embodiments, the interleave controller 344 uses one of a variety of scheduling algorithms to ensure that the scarce resource (access to a bank) is most efficiently scheduled.
For other types of solid-state storage media 110, other types of commands and corresponding queues may be included without straying from the scope of the disclosure. The flexible nature of an FPGA solid-state storage controller 104 allows flexibility in what type of storage media is used. If flash memory were changed to another solid-state storage type, the bank interleave controller 344, storage bus controller 348, and MUX 350 could be altered to accommodate the media type without significantly affecting the data pipelines 106, 108 and other solid-state storage controller 104 functions.
In the embodiment depicted in FIG. 4A, the bank interleave controller 344 includes, for each bank 214, a read queue 410 for commands to read data from the solid-state storage media 110, a write queue 412 for write commands to the solid-state storage media 110, an erase queue 414 for commands to erase an erase block in the solid-state storage, and a management queue 416 for management operations. The bank interleave controller 344 also includes corresponding read, write, erase, and management agents 402, 404, 406, 408. In another embodiment, the control and status registers 340 and control queues 342 or similar components queue commands for data sent to the banks 214 of the solid-state storage media 110 without a bank interleave controller 344.
The agents 402, 404, 406, 408, in one embodiment, direct commands of the appropriate type destined for a particular bank 214a to the correct queue for the bank 214a. For example, the read agent 402 may receive a read command for bank-1 214b and directs the read command to the bank-1 read queue 410b. The write agent 404 may receive a write command to write data to a location in bank-0 214a of the solid-state storage media 110 and will then send the write command to the bank-0 write queue 412a. Similarly, the erase agent 406 may receive an erase command to erase an erase block in bank-1 214b and will then pass the erase command to the bank-1 erase queue 414b. The management agent 408 may receive management operations, status requests, and the like, such as a reset command or a request to read a configuration register of a bank 214, such as bank-0 214a. The management agent 408 sends the management operation to the bank-0 management queue 416a. 
The agents 402, 404, 406, 408, in one embodiment, also monitor status of the queues 410, 412, 414, 416 and send status, interrupt, or other messages when the queues 410, 412, 414, 416 are full, nearly full, non-functional, etc. In one embodiment, the agents 402, 404, 406, 408 receive commands and generate corresponding sub-commands. In one embodiment, the agents 402, 404, 406, 408 receive commands through the control & status registers 340 and generate corresponding sub-commands which are forwarded to the queues 410, 412, 414, 416. In light of this disclosure, other functions of the agents 402, 404, 406, 408 may be possible.
The queues 410, 412, 414, 416 may receive commands and store the commands until required to be sent to the solid-state storage banks 214. In one embodiment, the queues 410, 412, 414, 416 are first-in, first-out (“FIFO”) registers or a similar component that operates as a FIFO. In another embodiment, the queues 410, 412, 414, 416 store commands in an order that matches data, order of importance, or other criteria.
In one embodiment, the bank interleave controller 344 may coordinate with the agents 402, 404, 406, 408 to monitor storage requests received by the control and status registers 340. In certain embodiments, the bank interleave controller 344 may monitor storage requests to identify the storage requests and determine whether the ordering of the storage request in the queues 410, 412, 414, 416 satisfy an operation order criteria. An operation order criteria is criteria for controlling the order of operation execution within the solid-state storage controller 104. In one embodiment, the order of operation execution may be managed by the bank interleave controller 344.
The bank controllers 418 may receive commands from the queues 410, 412, 414, 416 and generate appropriate subcommands. For example, the bank-0 write queue 412a may receive a command to write a page of data packets to bank-0 214a. The bank-0 controller 418a may receive the write command at an appropriate time and may generate one or more write subcommands for each data packet stored in the write buffer 320 to be written to the page in bank-0 214a. For example, bank-0 controller 418a may generate commands to validate the status of bank 0 214a and the solid-state storage array 216, select the appropriate location for writing one or more data packets, clear the input buffers within the solid-state storage memory array 216, transfer the one or more data packets to the input buffers, program the input buffers into the selected location, verify that the data was correctly programmed, and if program failures occur do one or more of interrupting the master controller 224, retrying the write to the same physical location, and retrying the write to a different physical location. In certain embodiments, the subcommands comprise multi-phase commands. Additionally, in conjunction with example write command, the storage bus controller 348 will cause the one or more commands to be multiplied to each of the storage I/O buses 210a-n with the logical address of the command mapped to a first physical addresses for storage I/O bus 210a, and mapped to a second physical address for storage I/O bus 210b, and so forth as further described below.
Bus arbiter 420 may select from among the bank controllers 418 and pulls subcommands from output queues within the bank controllers 418 and forwards these to the Storage Bus Controller 348 in a sequence that optimizes the performance of the banks 214. As described above, the bus arbiter 420 cooperates with the bank interleave controller 344 such that the desired operation execution order is accomplished. Of course re-adjusting execution order may be performed by ordering operations in a bank queue 418 or defining an order or prioritization for how the bus arbiter 420 selects the operations from a bank queue 418. In another embodiment, the bus arbiter 420 may respond to a high-level interrupt and modify the normal selection criteria. In another embodiment, the master controller 224 can control the bus arbiter 420 through the control and status registers 340. In further embodiments, the bus arbiter 420 may control and interleave the sequence of commands from the bank controllers 418 to the solid-state storage media 110 using other means.
The bus arbiter 420 may coordinate selection of appropriate commands, and corresponding data when required for the command type, from the bank controllers 418 and sends the commands and data to the storage bus controller 348. The bus arbiter 420, in certain embodiments, also sends commands to the storage control bus 212 to select the appropriate bank 214. For the case of flash memory or other solid-state storage media 110 with an asynchronous, bi-directional serial storage I/O bus 210, only one command (control information) or set of data can be transmitted at a time. For example, when write commands or data are being transmitted to the solid-state storage media 110 on the storage I/O bus 210, read commands, data being read, erase commands, management operations, or other status commands cannot be transmitted on the storage I/O bus 210. For example, when data is being read from the storage I/O bus 210, data cannot be written to the solid-state storage media 110.
For example, during a write operation on bank-0 the bus arbiter 420 selects the bank-0 controller 418a which may have a write command or a series of write sub-commands on the top of its queue, which cause the storage bus controller 348 to execute the following sequence. The bus arbiter 420 forwards the write command to the storage bus controller 348, which sets up a write command by selecting bank-0 214a through the storage control bus 212, sending a command to clear the input buffers of the solid-state storage elements 110 associated with the bank-0 214a, and sending a command to validate the status of the solid-state storage elements 216, 218, 220 associated with the bank-0 214a. The storage bus controller 348 then transmits a write subcommand on the storage I/O bus 210, which contains the physical addresses including the address of the logical erase block for each individual physical erase block of solid-stage storage element 216a-m as mapped from the logical erase block address. The storage bus controller 348 then multiplexes the write buffer 320 through the write synchronization buffer 308 to the storage I/O bus 210 through the MUX 350 and streams write data to the appropriate page. When the page is full, then storage bus controller 348 causes the solid-state storage elements 216a-m associated with the bank-0 214a to program the input buffer to the memory cells within the solid-state storage elements 216a-m. Finally, the storage bus controller 348 validates the status to ensure that page was correctly programmed.
A read operation is similar to the write example above. During a read operation, the bus arbiter 420, or other component of the bank interleave controller 344, receives data and corresponding status information and sends the data to the read data pipeline 108 while sending the status information on to the control and status registers 340. A read data command forwarded from bus arbiter 420 to the storage bus controller 348 may cause the MUX 350 to gate the read data on storage I/O bus 210 to the read data pipeline 108 and send status information to the appropriate control and status registers 340 through the status MUX 422.
The bus arbiter 420 coordinates the various command types and data access modes so that only an appropriate command type or corresponding data is on the bus at any given time. If the bus arbiter 420 has selected a write command, and write subcommands and corresponding data are being written to the solid-state storage media 110, the bus arbiter 420 will not allow other command types on the storage I/O bus 210. Beneficially, the bus arbiter 420 uses timing information, such as predicted command execution times, along with status information received concerning bank 214 status to coordinate execution of the various commands on the bus with the goal of minimizing or eliminating idle time of the busses.
The master controller 224 through the bus arbiter 420 may use expected completion times of the commands stored in the queues 410, 412, 414, 416, along with status information, so that when the subcommands associated with a command are executing on one bank 214a, other subcommands of other commands are executing on other banks 214b-n. When one command is fully executed on a bank 214a, the bus arbiter 420 directs another command to the bank 214a. The bus arbiter 420 may also coordinate commands stored in the queues 410, 412, 414, 416 with other commands that are not stored in the queues 410, 412, 414, 416.
For example, an erase command may be sent out to erase a group of erase blocks within the solid-state storage media 110. An erase command may take 10 to 1000 times more time to execute than a write or a read command or 10 to 100 times more time to execute than a program command. For N banks 214, the bank interleave controller 344 may split the erase command into N commands, each to erase a logical erase block of a bank 214a. While Bank 0 214a is executing an erase command, the bus arbiter 420 may select other commands for execution on the other banks 214b-n. The bus arbiter 420 may also work with other components, such as the storage bus controller 348, the master controller 224, etc., to coordinate command execution among the buses. Coordinating execution of commands using the bus arbiter 420, bank controllers 418, queues 410, 412, 414, 416, and agents 402, 404, 406, 408 of the bank interleave controller 344 can dramatically increase performance over other solid-state storage systems without a bank interleave function.
FIG. 4B is a schematic block diagram illustrating an alternate embodiment 401 of a bank interleave controller in the solid-state storage controller. The components 210, 212, 340, 346, 348, 350, 402-430 depicted in the embodiment shown in FIG. 4B are substantially similar to the bank interleave apparatus 400 described in relation to FIG. 4A except that each bank 214 includes a single queue 432a-n and the read commands, write commands, erase commands, management operations, etc. for a bank (e.g., Bank-0 214a) are directed to a single queue 432a for the bank 214a. The queues 432, in one embodiment, are FIFO. In another embodiment, the queues 432 can have commands pulled from the queues 432 in an order other than the order they were stored. In another alternate embodiment (not shown), the read agent 402, write agent 404, erase agent 406, and management agent 408 may be combined into a single agent assigning commands to the appropriate queues 432a-n. 
In another alternate embodiment (not shown), commands are stored in a single queue where the commands may be pulled from the queue in an order other than how they are stored so that the bank interleave controller 344 can execute a command on one bank 214a while other commands are executing on the remaining banks 214b-n. In further embodiments, other queue configurations and types may be used to enable execution of a command on one bank 214a while other commands are executing on other banks 214b-n. 
In one embodiment, the solid-state controller 104 includes one bank interleave controller 344 that serves all of the storage elements 216, 218, 220 of the solid-state storage media 110. In another embodiment, the solid-state controller 104 includes a bank interleave controller 344 for each column of storage elements 216a-m, 218a-m, 220a-m. For example, one bank interleave controller 344 serves one column of storage elements SSS 0.0-SSS N.0 216a, 218a, . . . 220a, a second bank interleave controller 344 serves a second column of storage elements SSS 0.1-SSS N.1 216b, 218b, . . . 220b etc.
The solid-state storage controller 104 includes a synchronization buffer 346 that buffers commands and status messages sent and received from the solid-state storage media 110. The synchronization buffer 346 is located at the boundary between the solid-state storage clock domain and the local bus clock domain and provides buffering to account for the clock domain differences. The synchronization buffer 346, write synchronization buffer 308, and read synchronization buffer 328 may be independent or may act together to buffer data, commands, status messages, etc. In one embodiment, the synchronization buffer 346 is located where there are the fewest number of signals crossing the clock domains. Synchronization between clock domains may be arbitrarily moved to other locations within the solid-state storage device 102 in order to optimize some aspect of design implementation.
The solid-state storage controller 104 includes a storage bus controller 348 that interprets and translates commands for data sent to and read from the solid-state storage media 110 and status messages received from the solid-state storage media 110 based on the type of solid-state storage media 110. For example, the storage bus controller 348 may have different timing requirements for different types of storage, storage with different performance characteristics, storage from different manufacturers, etc. The storage bus controller 348 also sends control commands to the storage control bus 212.
In one embodiment, the solid-state storage controller 104 includes a MUX 350 that comprises an array of multiplexers 350a-n where each multiplexer is dedicated to a row in the solid-state storage media 110. For example, multiplexer 350a is associated with solid-state storage elements 216a, 218a, 220a. MUX 350 routes the data from the write data pipeline 106 and commands from the storage bus controller 348 to the solid-state storage media 110 via the storage I/O bus 210 and routes data and status messages from the solid-state storage media 110 via the storage I/O bus 210 to the read data pipeline 108 and the control and status registers 340 through the storage bus controller 348, synchronization buffer 346, and bank interleave controller 344.
In one embodiment, the solid-state storage controller 104 includes a MUX 350 for each column of solid-state storage elements (e.g., SSS 0.0 216a, SSS 1.0 218a, SSS N.0 220a). A MUX 350 combines data from the write data pipeline 106 and commands sent to the solid-state storage media 110 via the storage I/O bus 210 and separates data to be processed by the read data pipeline 108 from commands. Packets stored in the write buffer 320 are directed on busses out of the write buffer 320 through a write synchronization buffer 308 for each column of solid-state storage elements (SSS 0.x to SSS N.x 216, 218, 220) to the MUX 350 for each column of solid-state storage elements (SSS 0.x to SSS N.x 216, 218, 220). The commands and read data are received by the MUXes 350 from the storage I/O bus 210. The MUXes 350 also direct status messages to the storage bus controller 348.
The storage bus controller 348 includes a mapping module 424. The mapping module 424 maps a logical address of an erase block to one or more physical addresses of an erase block. For example, a solid-state storage media 110 with an array of twenty storage elements (e.g., SSS 0.0 to SSS 0.M 216) per bank 214a may have a logical address for a particular logical erase block mapped to twenty physical addresses of twenty physical erase blocks, one physical address per storage element. Because the storage elements are accessed in parallel, erase blocks at the same position in each storage element in a column of storage elements 216a, 218a, 220a will have the same physical address. To select one erase block (e.g., in storage element SSS 0.0 216a) instead of all erase blocks in the column (e.g., in storage elements SSS 0.0, SSS 1.0, . . . SSS N.0 216a, 218a, 220a), one bank (in this case Bank 0 214a) is selected.
This logical-to-physical mapping for erase blocks is beneficial because if one physical erase block becomes damaged or inaccessible, the mapping can be changed so that the logical erase block maps to another physical erase block instead of the damaged physical erase block. This mitigates the impact of losing an entire logical erase block when one element's physical erase block is faulty. The remapping module 430 changes a mapping of a logical address of a logical erase block to one or more physical addresses of a physical erase blocks making up the logical erase block (the physical erase blocks being spread over the array of storage elements). A logical erase block may be mapped to a set of physical erase blocks in a single bank. For example, logical erase block 1 may be mapped to physical erase block 1 of storage element SSS 0.0 216a, to physical erase block 1 of storage element SSS 0.1 216b, . . . , and to physical erase block 1 of storage element SSS 0.M 216m; logical erase block 2 may be mapped to physical erase block 2 of storage element SSS 1.0 218a, to physical erase block 2 of storage element SSS 1.1 218b, . . . , and to logical erase block 2 of storage element 1.M 218m, etc. Alternatively, a logical erase block may be mapped to a set of physical erase blocks located in multiple banks. For example, logical erase block 1 may be mapped to one physical erase block from each storage element in an array such that logical erase block 1 includes physical erase blocks from Bank 0 214a (e.g., physical erase block 1 of storage element SSS 0.0 216a, physical erase block 1 of storage element SSS 0.1 216b, . . . , and physical erase block 1 of storage element 0.M 216m), physical erase blocks from Bank 1 214b (e.g., physical erase block 1 of storage element SSS 1.0 218a, physical erase block 1 of storage element SSS 1.1 218b, . . . , and physical erase block 1 of storage element 1.M 218m), and so on up to physical erase blocks from Bank N 214n, which may include, for example erase block 1 of storage element N.M 220m. 
If, for example, erase block 1 of storage element SSS 0.0 216a is damaged, experiencing errors due to wear, etc., or cannot be used for some reason, the remapping module 430 could change the logical-to-physical mapping for the logical address of logical erase block 1 that pointed to physical erase block 1. If a spare physical erase block (call it erase block 221) of storage element SSS 0.0 216a is available and currently not mapped, the remapping module 430 could change the mapping of logical erase block 1 to point to physical erase block 221 of storage element SSS 0.0 216a, while continuing to point to physical erase block 1 of storage element SSS 0.1 216b, physical erase block 1 of storage element SSS 0.2 216c (not shown) . . . , and physical erase block 1 of storage element M.0 216m. The mapping module 424 or remapping module 430 could map erase blocks in a prescribed order (e.g., logical erase block 1 to physical erase block 1 of the storage elements, logical erase block 2 to physical erase block 2 of the storage elements, etc.) or may map physical erase blocks of the storage elements 216, 218, 220 in another order based on some other criteria.
In one embodiment, the physical erase blocks could be grouped into a logical erase block by access time. Grouping by access time, meaning time to execute a command, such as programming (writing) data into pages of specific physical erase blocks, can level command completion so that a command executed across the physical erase blocks of a logical erase block is not limited by the slowest physical erase block. In other embodiments, the physical erase blocks may be grouped into a logical erase block by wear level, health, etc. In light of this disclosure, other factors other factors may be considered when mapping or remapping physical erase blocks into logical erase blocks.
In one embodiment, the storage bus controller 348 includes a status capture module 426 that receives status messages from the solid-state storage media 110 and sends the status messages to the status MUX 422. In another embodiment, when the solid-state storage media 110 is flash memory, the storage bus controller 348 includes a NAND bus controller 428. The NAND bus controller 428 directs commands from the read and write data pipelines 106, 108 to the correct location in the solid-state storage media 110, coordinates timing of command execution based on characteristics of the flash memory, etc. If the solid-state storage media 110 is another solid-state storage type, the NAND bus controller 428 would be replaced by a bus controller specific to the storage type. In further embodiments, the NAND bus controller 428 may perform other functions.
FIG. 5 is a schematic block diagram illustrating a logical representation 500 of a solid-state storage controller 506 with a logical-to-physical translation layer 512. The storage controller 506 may be similar, in certain embodiments, to the solid-state storage controller 104 depicted in FIG. 1 and may include one or more solid-state storage controllers 104. The depicted embodiment shows a user application 502 in communication with a storage client 504. The storage client 504 is in communication with a storage controller 506 that includes the logical-to-physical translation layer 512, an ECC correction module 514, a read data pipeline 516, and a write data pipeline 518.
The storage controller 506 manages solid-state storage media 110. The storage controller 506 may include various hardware and software controllers, drivers, and software, such as the depicted hardware controllers 520.
In one embodiment, the depicted hardware controllers 520 may be substantially similar to and include similar functionality as the solid-state controllers 104 and accompanying controllers and modules depicted in FIGS. 1 and 2 and/or the bank interleave controller 344 and storage bus controller 348 depicted in FIGS. 3, 4A, and 4B. Furthermore, the ECC correction module 514 may be substantially similar and include similar functionality to the ECC correction module 322 and/or the ECC generator 304 depicted in FIG. 3. In addition, the read data pipeline 516 and the write data pipeline 518 may be substantially similar to the read data pipeline 108 and the write data pipeline 106 depicted in FIG. 3. The solid-state storage array may include an array of solid-state storage banks similar to the solid-state storage media 110 and corresponding solid-state storage banks 214 depicted in FIG. 2.
In one embodiment, the user application 502 is a software application operating on or in conjunction with the storage client 504. The storage client 504 manages files and data and utilizes the functions and features of the storage controller 506 and associated solid-state storage array. Representative examples of storage clients include, but are not limited to, a server, a file system, an operating system, a database management system (“DBMS”), a volume manager, and the like. The storage client 504 is in communication with the storage controller 506. In one embodiment, the storage client 504 communicates through an Input/Output (I/O) interface represented by a block I/O emulation layer 508.
Certain conventional block storage devices divide the storage media into volumes or partitions. Each volume or partition may include a plurality of sectors. One or more sectors are organized into a logical block. In certain storage systems, such as those interfacing with the Windows® operating systems, the logical blocks are referred to as clusters. In other storage systems, such as those interfacing with UNIX, Linux, or similar operating systems, the logical blocks are referred to simply as blocks. A logical block or cluster represents a smallest physical amount of storage space on the storage media that is managed by the storage manager. A block storage device may associate n logical blocks available for user data storage across the storage media with a logical block address, numbered from 0 to n. In certain block storage devices, the logical block addresses may range from 0 to n per volume or partition. In conventional block storage devices, a logical block address maps directly to a particular logical block. In conventional block storage devices, each logical block maps to a particular set of physical sectors on the storage media.
However, certain storage devices 102 do not directly or necessarily associate logical block addresses with particular physical blocks. These storage devices 102 may emulate a conventional block storage interface to maintain compatibility with block storage clients 504.
When the storage client 504 communicates through the block I/O emulation layer 508, the storage device 102 appears to the storage client 504 as a conventional block storage device. In one embodiment, the storage controller 506 provides a block I/O emulation layer 508, which serves as a block device interface, or API. In this embodiment, the storage client 504 communicates with the storage device 102 through this block device interface. In one embodiment, the block I/O emulation layer 508 receives commands and logical block addresses from the storage client 504 in accordance with this block device interface. As a result, the block I/O emulation layer 508 provides the storage device 102 compatibility with block storage clients 504.
In one embodiment, a storage client 504 communicates with the storage controller 506 through a direct interface layer 510. In this embodiment, the storage device 102 directly exchanges information specific to non-volatile storage devices. A storage device 102 using direct interface 510 may store data on the solid-state storage media 110 as blocks, sectors, pages, logical blocks, logical pages, erase blocks, logical erase blocks, ECC chunks, logical ECC chunks, or in any other format or structure advantageous to the technical characteristics of the solid-state storage media 110. The storage controller 506 receives a logical address and a command from the storage client 504 and performs the corresponding operation in relation to the non-volatile solid-state storage media 110. The storage controller 506 may support a block I/O emulation layer 508, a direct interface 510, or both a block I/O emulation layer 508 and a direct interface 510.
As described above, certain storage devices, while appearing to a storage client 504 to be a block storage device, do not directly associate particular logical block addresses with particular physical blocks, also referred to in the art as sectors. Such storage devices may use a logical-to-physical translation layer 512. The logical-to-physical translation layer 512 provides a level of abstraction between the logical block addresses used by the storage client 504, and the physical block addresses at which the storage controller 506 stores the data. The logical-to-physical translation layer 512 maps logical block addresses to physical block addresses of data stored on solid-state storage media 110. This mapping allows data to be referenced in a logical address space using logical identifiers, such as a logical block address. A logical identifier does not indicate the physical location of data on the solid-state storage media 110, but is an abstract reference to the data.
The storage controller 506 manages the physical block addresses in the physical address space. In one example, contiguous logical block addresses may in fact be stored in non-contiguous physical block addresses as the logical-to-physical translation layer 512 determines the location on the solid-state storage media 110 to perform data operations.
Furthermore, in one embodiment, the logical address space is substantially larger than the physical address space. This “thinly provisioned” or “sparse address space” embodiment, allows the number of logical identifiers for data references to greatly exceed the number of possible physical addresses. Specifically, the logical address space may be “sparse” and, as such, may comprise a logical capacity that exceeds the physical storage capacity of the solid-state storage media 110. Accordingly, the logical address space may be defined independent of the solid-state storage media 110; the logical address space may present a larger address space than the physical storage capacity of the solid-state storage media 110, may present different storage location partitions and/or block sizes than provided by the solid-state storage media 110, and so on.
The storage controller 506 may support a sparse address space by writing data using a log-based, append only writing structure. Specifically, the storage controller 506, in one embodiment, writes data of a write request to physical storage media of the solid-state storage media 110 at one or more logical addresses of the physical storage media corresponding to the addresses of the write request as mapped by the logical-to-physical translation layer 512. In a further embodiment, the storage controller 506 writes the data of the write request by appending the data to a sequential, log-based writing structure of the physical storage media of the solid-state storage media 110 at an append point. The storage controller 506, in one embodiment, returns one or more physical addresses corresponding to the append point and the logical-to-physical translation layer 512 maps the one or more logical addresses to the one or more physical addresses corresponding to the append point.
As the storage controller 506 clears, trims, replaces, expires, and/or evicts, data from the physical addresses and associated physical storage media, the solid-state storage media 110 in the depicted embodiment, are freed to store data for other logical addresses. In one embodiment, the storage controller 506 stores data at the physical addresses using a log-based, append only writing structure such that data overwritten by a subsequent write request invalidates other data in the log. Consequently, a garbage collection process recovers the physical capacity of the invalid data in the log. One embodiment of the log-based, append only writing structure is a logically ring-like data structure, as new data is appended to the log-based writing structure, previously used physical capacity is reused in a circular, theoretically infinite manner.
In one embodiment, the logical-to-physical translation layer 512 includes a map or index, a “forward map,” that maps logical block addresses to physical block addresses. Often logical addresses used to identify stored data represent a very small number of logical addresses that are possible within a name space or range of possible logical addresses. Searching this sparsely populated space may be cumbersome. For this reason, the forward map may comprise a data structure that facilitates quickly traversing the forward map to find a physical address based on a logical address. For example, the forward map may include a B-tree, a content addressable memory (“CAM”), a binary tree, a hash table, or other data structure that facilitates quickly searching a sparsely populated space or range. By using a forward map that quickly searches a sparsely populated logical namespace or address space, the logical-to-physical translation layer 512 provides an efficient way to determine one or more physical addresses from a logical address. In certain embodiments, the logical-to-physical translation layer 512 is a tree with nodes that represent logical block addresses and comprise corresponding physical block addresses.
In one embodiment, the forward map binds, in a logical-to-physical map, bound LBAs to physical storage locations. The storage controller 506 may determine if the logical space has sufficient unallocated logical space using the logical-to-physical map. The logical-to-physical map may be used to track allocation of bound LBAs, unbound LBAs, allocated LBAs, unallocated LBAs, allocated LBA capacity, unallocated LBA capacity, and the like. In one embodiment, the forward map binds LBAs to corresponding physical storage location addresses in multiple maps.
The forward map, the sparse logical address space, and the log-based writing are described in further detail in U.S. patent application Ser. No. 12/986,117 entitled “Apparatus, System, and Method for a Virtual Storage Layer” filed 6 Jan. 2011, for David Flynn et al., and U.S. Provisional Patent Application Ser. No. 61/373,271 entitled “Apparatus, System, and Method for Caching Data” filed 12 Aug. 2010, for David Flynn, which are hereby incorporated by reference.
As stated above, in conventional block storage devices, a logical block address maps directly to a particular physical block. When a storage client 504 communicating with the conventional block storage device deletes data for a particular logical block address, the storage client 504 may note that the particular logical block address is deleted and can re-use the physical block associated with that deleted logical block address without the need to perform any other action.
Conversely, when a storage client 504, communicating with a storage controller 104 with a logical-to-physical translation layer 512 (a storage controller 104 that does not map a logical block address directly to a particular physical block), deletes a logical block address, the corresponding physical block address remains allocated because the storage client 504 does not communicate the change in used blocks to the storage controller 506. The storage client 504 may not be configured to communicate changes in used blocks (also referred to herein as “data block usage information”). Because the storage client 504 uses the block I/O emulation 508 layer, the storage client 504 may erroneously believe that the storage controller 506 is a conventional storage controller that would not utilize the data block usage information. Or, in certain embodiments, other software layers between the storage client 504 and the storage controller 506 may fail to pass on data block usage information.
Consequently, the storage controller 104 preserves the relationship between the logical block address and a physical address and the data on the storage device 102 corresponding to the physical block. As the number of allocated blocks increases, the performance of the storage controller 104 may suffer depending on the configuration of the storage controller 104.
Specifically, in certain embodiments, the storage controller 506 is configured to store data sequentially, using an append-only writing process, and use a storage space recovery process that re-uses non-volatile storage media storing deallocated/unused logical blocks. Specifically, as described above, the storage controller 506 may sequentially write data on the solid-state storage media 110 in a log structured format and within one or more physical structures of the storage elements, the data is sequentially stored on the solid-state storage media 110.
As a result of storing data sequentially and using an append-only writing process, the storage controller 506 achieves a high write throughput and a high number of I/O operations per second (“IOPS”). The storage controller 506 includes a storage space recovery, or garbage collection process that re-uses data storage cells to provide sufficient storage capacity. The storage space recovery process reuses storage cells for logical blocks marked as deallocated, invalid, unused, or otherwise designated as available for storage space recovery in the logical-physical translation layer 512.
Returning now to FIG. 1, in one embodiment, the storage controller 104 sequentially writes data on the solid-state storage media 110 in a log structured format and within one or more physical structures of the storage elements, the data is sequentially stored on the solid-state storage media 110. Sequentially writing data involves the storage controller 104 streaming data packets into storage write buffers for storage elements, such as a chip (a package of one or more dies) or a die on a circuit board. When the storage write buffers are full, the data packets are programmed to a designated virtual or logical page (“LP”) at a head of the log-based structure. Data packets then refill the storage write buffers and, when full, the data packets are written to the head of the log, which is advanced to the next LP of a logical erase block. The next virtual page may be in the same bank 214a or another bank (e.g. 214b). This process continues, LP after LP, until the logical erase block (“LEB”) is filled, or the like. The head of the log advances sequentially through the logical pages of the logical erase block of solid-state storage media 110 according to a predetermined write order of the logical erase block (which may be related to a write order specified by a manufacturer of the solid-state storage elements of solid-state storage media 110) during the appending of the data packets.
A means for writing a plurality of data packets to a storage medium 110 by sequentially appending the data packets to a log-based structure of the storage medium, in various embodiments, may include a storage controller 104, an indexing module 120, a write agent 404, a storage controller 506, a hardware controller 520, a device driver installed for the storage device 102 on the host computing system 114, other logic hardware, and/or other executable code stored on a computer readable storage medium. Other embodiments may include similar or equivalent means for writing a plurality of data packets to a storage medium 110.
By sequentially appending the data packets to the head of the log, an ordered sequence of storage operations completed on the solid-state storage media 110 is preserved on solid-state storage media 110 since the data packets are written to sequential, contiguous physical locations of solid-state storage media in the same order that the write operations are performed. LPs and LEBs are described in more detail below.
In another embodiment, the streaming may continue across LEB boundaries with the process continuing, LEB after LEB. The storage controller 104, in certain embodiments, sequentially stores data packets in an LEB by order of processing. In one embodiment, where a write data pipeline 106 is used, the storage controller 104 stores packets in the order that they come out of the write data pipeline 106. This order may be a result of data segments arriving from a requesting device mixed with packets of valid data that are being read from another storage location as valid data is being recovered from another LEB during a recovery operation.
The sequentially stored data, in one embodiment, can serve as a log to reconstruct data indexes and other metadata using information from data packet headers. For example, in one embodiment, the storage controller 104 may reconstruct a storage index by reading headers to determine the data structure to which each packet belongs and sequence information to determine where in the data structure the data or metadata belongs. The storage controller 104, in one embodiment, uses physical address information for each packet and timestamp or sequence information to create a mapping between the physical locations of the packets and the data structure identifier and data segment sequence. Timestamp or sequence information is used by the storage controller 104 to replay the sequence of changes made to the index and thereby reestablish the most recent state.
In one embodiment, erase blocks are time stamped or given a sequence number as packets are written and the timestamp or sequence information of an erase block is used along with information gathered from container headers and packet headers to reconstruct the storage index. In another embodiment, timestamp or sequence information is written to an erase block when the erase block is recovered.
In a read, modify, write operation, data packets associated with requested data are located and read in a read operation. Data segments of the modified structure that have been modified are not written to the location from which they are read. Instead, the modified data segments are again converted to data packets and then written to the next available location in the virtual page currently being written. Index entries for the respective data packets are modified to point to the packets that contain the modified data segments. The entry or entries in the index for data packets associated with the same requested data that has not been modified will include pointers to original location of the unmodified data packets. Thus, if the original requested data is maintained, for example to maintain a previous version of the requested data, the original requested data will have pointers in the index to all data packets as originally written. The new requested data will have pointers in the index to some of the original data packets and pointers to the modified data packets in the virtual page that is currently being written.
In a copy operation, the index includes an entry for the original requested data mapped to a number of packets stored on the solid-state storage media 110. When a copy is made, a new copy of the requested data is created and a new entry is created in the index mapping the new copy of the requested data to the original packets. The new copy of the requested data is also written to the solid-state storage media 110 with its location mapped to the new entry in the index. The new copy of the requested data packets may be used to identify the packets within the original requested data that are referenced in case changes have been made in the original requested data that have not been propagated to the copy of the requested data and the index is lost or corrupted. In another embodiment, the index includes a logical entry for a logical block.
Beneficially, sequentially writing packets facilitates a more even use of the solid-state storage media 110 and allows the solid-storage device controller 202 to monitor storage hot spots and level usage of the various virtual pages in the solid-state storage media 110. Sequentially writing packets also facilitates a powerful, efficient garbage collection system, which is described in detail above.
The system 100 may comprise a log-structured storage system or log-structured array similar to a log-structured file system and the order that data is stored may be used to recreate an index. An index that includes a logical-to-physical mapping, in one embodiment, is stored in volatile memory. If the index is corrupted or lost, the index may be reconstructed by addressing the solid-state storage media 110 in the order that the data was written. Within a logical erase block (“LEB”), data may be stored sequentially by filling a first logical page, then a second logical page, etc. until the LEB is filled. The solid-state storage controller 104 then chooses another LEB and the process repeats. By maintaining an order that the LEBs were written to and by knowing that each LEB is written sequentially, the index can be rebuilt by traversing the solid-state storage media 110 in order from beginning to end. In other embodiments, if part of the index is stored in non-volatile memory, such as on the solid-state storage media 110, the solid-state storage controller 104 may only need to replay a portion of the solid-state storage media 110 to rebuild a portion of the index that was not stored in non-volatile memory.
As was described above, the forward map provides a logical-to-physical mapping of logical block addresses to physical locations on solid-state storage media 110. The forward map may be stored in a number of different ways. For example, the forward map may be stored in nonvolatile memory (e.g., RAM). Due to the importance of the forward map, the information in the forward map may be stored redundantly so that if the forward map is lost it may be re-created from the redundant information.
In one embodiment, data packets written to solid-state storage media 110 include information from which the forward map may be re-created. Each data packet may include a header containing the logical block address associated with the data packet. If the forward map is lost, storage controller 104 may recover the forward map by first reading the headers of the data packets stored on solid-state storage media 110 to determine the logical block address associated with the data packets stored on solid-state storage media 110. For each data packet, storage controller 104 may read the header of the data packet and extract the logical block address from the header. Storage controller 104 may then associate the extracted logical block address with the physical address of solid-state storage media 110 from which storage controller 104 read the data packet. Storage controller 104 may then associate the extracted logical block address with the physical address. This association then becomes one entry in the re-created forward map. This process is repeated for other data packets stored by solid-state storage media 110 until the forward map is re-created.
This method of re-creating the forward map may be time-consuming since storage controller 104 reads headers of all of the data packets stored on solid-state storage media 110 for which entries in the forward map are to be re-created. In certain embodiments, the smallest unit that can be read from the solid-state storage media 110 is a page. Thus, each page is read and then each data packet of each page to recreate the forward map. Reading the headers for a storage device holding 160 GB of data may take as long as 45 minutes. For a 230 GB device, that comes to about 1.5 hours.
In one embodiment, the recreation of the forward map takes less time because fewer storage media pages must be read in order to recreate the forward map. In one embodiment, only the header page, footer page, and pages holding the index segments are read. On average, the number of pages read to recreate the forward map may be reduced by as much as ninety percent or more.
An alternative method of re-creating the forward map may be used. According to this method, index segments are written to solid-state storage media 110. Each index segment contains information from which logical block addresses and corresponding physical addresses for a plurality of data packets can be determined. As a result, when re-creating a forward map, storage controller 104 need only read the one index segment to determine logical block addresses and corresponding physical addresses for the plurality of data packets represented by the one index segment.
A single erase block (e.g., logical erase block) of solid-state storage media 110, may include a plurality of index segments, each of which contain information from which forward map entries for a plurality of data packets may be determined. As a result, when re-creating the forward map for data packets stored in the single erase block, storage controller 104 need only read the pages that hold index segments of the single erase block rather than reading the headers of all of the data packets stored in the single erase block. Using this approach, the number of reads that storage controller 104 performs to retrieve information used to re-create forward map entries for the single erase block is significantly reduced (by as much as 90%) as compared with the method described above in which the header of each data packet in the single erase block is read. In one embodiment, all data packets stored in the single erase block are described by index segments that are also stored in the single erase block. Consequently, storage controller 104 may re-create the forward map for the data packets of the single erase block without having to read from erase blocks other than the single erase block. This may be advantageous since, as was described above, erase blocks may be recovered for rewriting through a garbage collection process. By keeping index segments for a given erase block in the same erase block that they describe, the erase block itself becomes a boundary for separating index segments on the storage device. Consequently, this independence means there is no need to move index segments to another erase block if a particular erase block is about to be erased and its valid data is being copied to a different erase block. The copied forward data will simply get included in a new index segment for that different erase block.
As illustrated in FIG. 1, storage controller 104 may include an indexing module 120. Indexing module 120 may determine the contents of each index segment and write the index segments to solid-state storage media 110. In one embodiment, the indexing module 120 may include logic hardware, such as a processor, an FPGA, an ASIC, custom logic, discrete electronic components, or other logic hardware of the host computing device 114 and/or of the storage device 102. In another embodiment, the indexing module 120 may include executable code stored on a computer readable storage medium, such as a device driver for the storage device 102 installed on the host computing system 114 for execution on a processor of the host computing system 114 or the like. In a further embodiment, the indexing module 120 may include a combination of both logic hardware and executable code.
A means for writing an index segment associated with a plurality of data packets to a log-based structure of a storage medium 110, in various embodiments, may include a storage controller 104, an indexing module 120, a write agent 404, a storage controller 506, a hardware controller 520, a device driver installed for the storage device 102 on the host computing system 114, other logic hardware, and/or other executable code stored on a computer readable storage medium. Other embodiments may include similar or equivalent means for writing an index segment associated with a plurality of data packets.
Referring to FIG. 6, a logical erase block 602 is illustrated. Logical erase block 602 includes a plurality of data packets 604, 606, 608, 610, 612, 614, 616, and 640 written in logical pages 603. Logical erase block 602 also includes index segments 650, 652, and 654 as well as an index root 660. Data packets 604, 606, 608, 612, 614, 616, and 640; index segments 650, 652, and 654; and index root 660 are written in logical pages 603 of logical erase block 602.
Storage controller 104 writes packets received in write data pipeline 106 to solid-state storage media 110 by appending the packets to the head of the log-based structure as described above. Each data packet is associated with a different logical identifier. The logical identifiers belong to a logical address space that is independent of physical storage locations of solid-state storage media 110. In one embodiment, the logical address space may be a logical block address space comprising logical block addresses and the logical identifiers may be the logical block addresses.
The logical identifiers are independent of physical storage locations of solid-state storage media 110 since, as was described above, there is no fixed relationship between a logical identifier (e.g., logical block address) and a physical storage location (e.g., physical address) of solid-state storage media 110. Instead, any given logical identifier may be associated with substantially any physical storage location of solid-state storage media 110. The index described above keeps track of which logical identifiers are associated with which physical storage location of solid-state storage media 110.
Indexing module 120 builds index segments containing information from which the logical block identifiers of the packets may be determined. In one embodiment, indexing module 120 writes the index segments to the log-based structure. Each index segment may contain information from which the logical identifiers of some of the data packets written earlier in the log-based structure may be determined.
For example, data packets 604 may be written to logical erase block 602 prior to index segment 650a. Index segment 650a may contain identifier information from which logical identifiers (e.g., logical block addresses) of data packets 604 may be determined. Use of an identifier instead of the logical block address may conserve space on the media. Similarly, index segment 652a may contain identifier information from which logical identifiers of data packets 606 (which proceed index segment 652a in the log) may be determined. Note that indexing module 120 writes index segment 652a to logical erase block 602 after storage controller 104 has written data packets 606 to logical erase block 602. In one embodiment, an index segment may comprise the logical identifiers (e.g., logical block addresses) of each of the data packets that the index segment represents. For example, index segment 650a may comprise logical identifiers of each of data packets 604.
In another embodiment, an index segment may comprise identifier information from which the logical identifiers of each of the data packets that the index segment represents may be determined without actually storing each of the logical identifiers. In other words, the index segment may be free from the logical identifiers. This may be done to conserve storage space on the media.
In this embodiment, various methods may be used to reduce and/or compress the logical identifiers. According to one method, rather than storing a set of contiguous (e.g., consecutive) logical identifiers in an index entry, a starting logical identifier for the set and the number of contiguous logical identifiers in the set may be stored in the index entry together with a count for the number of consecutive/contiguous logical identifiers that follow. In this manner, an index entry may include identifier information representing a plurality of logical identifiers. The data associated with the contiguous logical identifiers may be referred to as an extent or a data extent. According to another method, some portions of the logical block addresses may be identical (for example the high order bits) and the method may include storing the identical portion of the logical block addresses once rather than for each of the logical block addresses. Other compression techniques are also possible including run length encoding of similar metadata (e.g., identifier information) and compression based on statistical examination of index entries or the like.
In addition to the identifier information describing the logical identifiers, an index segment may, in some embodiments, also include location information describing physical storage locations (e.g., physical addresses) on solid-state storage media 110 where the data packets represented by the index segment are located. In one embodiment, the location information represents a physical storage location without explicitly comprising the physical storage location. In one example, the index segment may include an offset for one or more of the data packets it represents where the offset is an offset from the location in which the index segment is stored. In another example, the location information may be an offset within a logical erase block or an offset within a logical page. In another embodiment, the location information comprises a count and the offset or physical storage location is derived by knowing the number of data packets represented by an index segment and multiplying that by the size of the data packets where the data packets are of a known fixed size. This information together with the ordering of index entries in an index segment may permit derivation of the physical storage location.
The index segment may also include type information (e.g., an opcode) indicating to which of a plurality of types each data packet represented by the index segment belongs. In one embodiment, index segments may also include sequence numbers identifying the sequence in which the index segments are written to the log-based structure.
In one embodiment, the index entries of an index segment may be said to create a storage operation context for data packets represented by the index segment. The storage operation context may include the physical storage location information and the identifier information. Indexing module 120 may determine a storage operation context for a data packet from the index segment representing the data packet.
Each index segment may be stored in solid-state storage media 110 as metadata in a page, data packet, ECC chunk, etc. The number and size of the index segments within a logical erase block may be controlled by indexing module 120.
In one embodiment, indexing module 120 may be configured to generate index segments having a substantially consistent size. As a result, indexing module 120 may accumulate identifier information describing logical identifiers and/or other information describing data packets written to solid-state storage media 110 until the information reaches a predetermined size at which point indexing module 120 may generate an index segment and write the index segment to solid-state storage media 110. Indexing module 120 may then continue to accumulate additional information and generate additional index segments. In one embodiment, the predetermined size is sufficient to store index entries for packets filling an amount of capacity equal to at least two of the smallest read units of solid-state storage media 110. If the predetermined size was only large enough to store index entries for packets filling an amount of capacity equal to one of the smallest read units of solid-state storage media 110, when recreating an index (described in more detail below), storage controller 104 may read a number of read units containing the index entries that is equal to the number of read units storing the packets represented by the index entries. Doing so would be no more efficient than just reading the read units storing the packets and thus would defeat the efficiencies sought by using the index entries. Accordingly, using a predetermined size sufficient to store index entries for packets filling an amount of capacity equal to at least two of the smallest read units of solid-state storage media 110 ensures efficiency gains when recreating an index.
In one embodiment, if the smallest read unit (the smallest amount of data that can be read in one read operation) of solid-state storage media 110 is a physical page, the predetermined size is large enough to store index entries filling two physical pages of solid-state storage media 110. In some cases, the predetermined size may be sufficient to store index entries for packets filling at least two logical pages of the solid-state storage media. The predetermined size may be user configurable.
Due to the ability to reduce and/or compress the logical identifiers described above, the number of data packets represented by each index segment may vary. For example, index segment 650a comprises identifier information from which the logical block addresses of data packets 604 (four data packets) may be determined while index segment 652a comprises identifier information from which the logical block addresses of data packets 606 (fourteen data packets) may be determined. This may be because data packets 606 include a number of data packets having contiguous logical block addresses (large data extents). FIG. 6 illustrates other examples. In particular, index segment 654a represents thirteen data packets (data packets 608), index segment 650b represents four data packets (data packets 610), index segment 652b represents eleven data packets (data packets 612), and index segment 654b represents six data packets (data packets 614).
In some embodiments, the number and size of index segments within the logical erase block may be configured by a user. The number and size may be chosen to minimize both an amount of time consumed in re-creating the forward map and an amount of interruption to the writing of data packets incurred by writing the index segments. To minimize the amount of time consumed in re-creating the forward map, indexing module 120 generates index segments each representing more than one data packet. As the number of data packets represented by each index segment increases, the number of index segments that need to be read to re-create the forward map decreases (because there are fewer index segments), thereby decreasing the amount of time consumed in re-creating the forward map. In one embodiment, each index segment represents at least two data packets.
On the other hand, as the number of data packets represented by each index segment increases, the size of each index segment also increases. As the size of the index segment increases, the amount of time it takes for storage controller 104 to write the index segment to solid-state storage media 110 also increases. Time that storage controller 104 spends in writing index segments to solid-state storage media 110 is time that storage controller 104 cannot use to write data packets to solid-state storage media 110. Accordingly, time spent in writing index segments decreases the effective throughput of storage controller 104.
This is particularly the case in embodiments in which the storage controller 104 writes the data to the media using a sequential, log-based, append only writing protocol that includes a single append point. If multiple append points are used the impact of writing large index segments may be mitigated by having an append point dedicated to writing metadata such as the index segments.
Thus, indexing module 120 may be configured by the user to generate index segments having a size such that writing the index segments to solid-state storage media 110 has a minimal effect on throughput yet provides a significant decrease in the amount of time consumed in re-creating a forward map. In one embodiment, indexing module 120 may be configured to generate index segments that are about 15% of the size of the largest possible page 603 of solid-state storage media 110.
In an alternative embodiment, rather than using index segments having a predetermined size, the index segments are different sizes and each index segment represents the an equal number of data packets.
Each index segment may comprise a plurality of index entries where each index entry represents one or more data packets. Indexing module 120 may preserve an order in which the index entries are created for the index segment. Storage controller 104 may later rely on this order. For example, storage controller 104 may write a data packet associated with a particular logical identifier to solid-state storage media 110 and may then immediately or shortly thereafter write a different data packet associated with the particular logical identifier and represented by the same index segment as the first data packet associated with the particular logical block address to the solid-state storage media 110 in order to change data associated with the particular logical identifier.
In this case, both data packets will be associated with the same logical identifier. In order for storage controller 104 to know which of the data packets is the “current” data packet, storage controller 104 may rely on the order the data entries are placed in the index segment to know which of the data packets was written to solid-state storage media 110 most recently. In doing so, storage controller 104 need only inspect the index segment associated with the two data packets and need not read the data packets themselves.
A similar situation may arise in which a data packet associated with the particular logical identifier is written to solid-state storage media 110 and is represented by index segment 650a and later a second data packet associated with the particular logical identifier is written to solid-state storage media 110 and is represented by a later index segment such as index segment 650b. Accordingly, when writing index segments to solid-state storage media 110, indexing module 120 may preserve an order in which the index segments are written. For example, indexing module 120 may form the index segments such that the index segments each include a sequence number indicating an order in which the index segments are written to solid-state storage media 110.
Additionally or alternatively, indexing module 120 may determine the order in which the index segments are written based on their position within a logical erase block. For example, indexing module 120 may determine that index segment 650a was written to solid-state storage media 110 prior to index segment 652a because index segment 650a occurs earlier in the write order of logical erase block 602. Another way of describing this is to say that index segment 650a occurs earlier in the log based structure of logical erase block 602 than index segment 652a because the logical erase block 602 is known to have been written sequentially in order of operation.
In one embodiment, the last index segment written to a logical erase block may have a different size than other index segments written to the same logical erase block because the last index segment may represent fewer data packets than the other index segments. The last index segment may be prevented from representing as many data packets as the other index segments because of its proximity to the end of the logical erase block and because the last index segment may be constrained to represent only data packets from the logical erase block and not data packets written in other logical erase blocks.
Furthermore, in contrast to the other index segments, the last index segment written to the logical erase block may be written earlier in the log-based structure than the data packets that the last index segment represents. This situation may arise, for example, when the last data packet written to the logical erase block spans more than one logical erase block. In this manner, data packets are still permitted to span more than one logical erase block and the collection of index segments in a single logical erase block only relates to a single logical erase block. Consequently, the collection of index segments for the single logical erase block is an independent and autonomous representation of data packets on the logical erase block. This allows for a single logical erase block to be managed without having dependencies to other logical erase blocks. This independence among index segments of a logical erase block allows the logical erase block to be erased without any dependency on another logical erase block that may delay the erasure of the logical erase block.
As indexing module 120 writes index segments to logical erase block 602, the locations of the index segments within logical erase block 602 are not necessarily known to the indexing module 120 ahead of time since the index segments are written to an append point of the log-based structure. In order for storage controller 104 to quickly find the index segments within a logical erase block, the positions of the index segments within the logical erase block should be known to storage controller 104 so that storage controller 104 does not need to scan through all of the pages 603 and/or data packets of the logical erase block to find the index segments.
In one embodiment, indexing module 120 writes an indexing root 660 to logical erase block 602. Indexing root 660 may contain information from which the positions of index segments 650, 652, and 654 within logical erase block 602 may be determined. In one embodiment, indexing root 660 may comprise a pointer to index segment 650N, index segment 650N may comprise a pointer to index segment 650b, index segment 650b may comprise a pointer to index segment 650a, and so on, so that each of the index segments is pointed to by either another index segment or index root 660. Consequently, storage controller 104 may quickly determine the positions of index segments 650, 652, and 654 within logical erase block 602 by reading index root 660 and following the pointers. In one embodiment, each pointer may include a starting offset within the logical erase block at which the index segment being pointed to begins and a length of the index segment being pointed to.
In one embodiment, index root 660 is stored in a predetermined location of logical erase block 602 and storage controller 104 knows the predetermined location. For example, index root 660 may be stored in the last logical page 603N of logical erase block 602. Note that index root 660 cannot be stored in the first logical page 603a of logical erase block 602 since logical erase block 602 must be written in order and at the time of writing the first logical page 603a of logical erase block 602 none of the positions of index segments 650, 652, and 654 will be known to storage controller 104. Accordingly, index root 660 may be written in a logical page 603N of logical erase block 602 that is subsequent to index segments 650, 652, and 654 in the write order of logical erase block 602. In an alternative embodiment, the index root 660 for a previous LEB may be stored in the first page of a subsequent logical erase block 602 since the previous logical erase block 602 will have been written in order and at the time of writing the first page of the next logical erase block 602 the positions of index segments in that previous LEB would be known to storage controller 104.
In one embodiment, index segments 650, 652, and 654 may be arranged in groups (e.g., eight groups). For example, index segments 650 may form a first group, index segment 652 may form a second group, and index segments 654 may form a third group. Index root 660 may point to at least one index segment of each group. This is illustrated in FIG. 7 in which index root 660 points to index segment 650N, index segment 652b, and index segment 654b. Furthermore, as illustrated, some index segments of a group may point to another index segment of the group. For example, index segment 650N points to index segment 650b, and index segment 650b points to index segment 650A.
If index segments are arranged into groups, storage controller 104, when reading the index segments, may read at least one index segment from each group simultaneously. For example, storage controller 104 may simultaneously read index segments 650N, 652b, and 654b if these index segments are stored on different elements of solid-state storage media 110 accessible in parallel. Reading these index segments simultaneously further reduces an amount of time consumed in reconstructing the forward map.
As illustrated in FIG. 6, index segments may be assigned to groups in a round robin fashion such that a first index segment 650a (occurring earliest in the log-based structure) is assigned to a first group 650, the index segment 652a occurring next in the log is assigned to the second group 652, the index segment 654a occurring next in the log is assigned to the third group 654, the index segment 650b occurring next in the log is assigned to the first group 650, and so on. Assigning index segments in this manner helps to increase the chances that the index segments will be stored in different banks of solid-state storage media 110 thereby enabling the index segments to be read from the different banks in parallel.
Note that as illustrated in FIG. 6, index segments 650, 652, and 654 are interspersed with data packets 604, 606, 608, 610, 612, 614, 616, and 640 within logical erase block 602. Since the index segments may be considered metadata because they comprise data that describes data rather than storing user data, logical erase block 602 can be said to store user data and interspersed metadata. Furthermore, note that logical erase block 602 may be stored across an array of physically distinct solid-state storage elements as discussed above in relation to FIG. 2.
As was mentioned above, if the forward map is lost or otherwise needs to be reconstructed, storage controller 104 may reconstruct the forward map using the index segments by first reading index root 660 to determine the locations of the index segments and then reading the individual index segments from the solid-state storage media 110 to retrieve the information regarding both the logical identifiers and physical storage locations on solid-state storage media 110 of the data packets.
In one embodiment, indexing module 120 may derive physical addresses of the solid-state storage media 110 for the data packets represented by the index segments from location information of the index segments and may derive the logical identifiers (e.g., logical block addresses) associated with data packets from identifier information of the index segments.
In some cases, storage controller 104 may determine upon reading one of the index segments that the index segment is not reliable. For example, the read index segment may be unreliable because it contains uncorrectable errors. In this case, storage controller 104 may read headers of each of the data packets represented by the unreliable index segment from solid-state storage media 110. Storage controller 104 may then extract and/or derive the logical identifiers and physical storage locations of the data packets represented by the unreliable index segment from the data packets themselves. Thus, redundantly storing the logical identifiers in headers of each of the data packets provides a redundant source of data from which the forward map may be reconstructed, if needed.
According to another embodiment, a forward map construction method includes storage controller 104 reading index segments from solid-state storage 110. Indexing module 120 derives locations on solid-state storage media 110 storing data packets represented by the index segments from location information of the index segments. Indexing module 120 also derives logical identifiers associated with the data packets from the index segments. In one embodiment, indexing module 120 may derive the logical identifiers without retrieving the data packets represented by the index segments from solid-state storage media 110. Indexing module 120 then builds a forward map for the data packets. Individual entries of the forward map specify the logical identifier of the data packet associated with the individual forward map entry and the location on solid-state storage media 110 storing the data packet associated with the individual forward map entry.
In one embodiment, storage controller 104 may read all of the index segments stored in the logical erase block prior to writing the forward map entries to the forward map. Furthermore, indexing module 120 may write the forward map entries to the forward map associated with the index segments in an order in which the index segments were written to the log-based structure. The index segments may each include a sequence identifier indicating an order in which the index segments were written to the log-based structure.
A means for reading index segments from the storage medium 110, a means for building a forward map that maps logical identifiers to physical locations of data packets, a means for deriving physical addresses of the storage medium 110 for data packets from location information in the read index segments, and/or a means for deriving logical identifiers associated with data packets from index segments, in various embodiments, may include a storage controller 104, an indexing module 120, a storage controller 506, a hardware controller 520, a device driver installed for the storage device 102 on the host computing system 114, other logic hardware, and/or other executable code stored on a computer readable storage medium. Other embodiments may include similar or equivalent means for reading index segments from the storage medium 110, building a forward map that maps logical identifiers to physical locations of data packets, deriving physical addresses of the storage medium 110 for data packets from location information in the read index segments, and/or deriving logical identifiers associated with data packets from index segments.
A means for determining that a written index segment is not reliable, a means for reading data packets represented by an unreliable index segment from the storage medium 110, and/or means for extracting logical identifiers associated with data packets represented by an unreliable index segment from the data packets, in various embodiments, may include a storage controller 104, an indexing module 120, a storage controller 506, a hardware controller 520, a device driver installed for the storage device 102 on the host computing system 114, other logic hardware, and/or other executable code stored on a computer readable storage medium. Other embodiments may include similar or equivalent means for determining that a written index segment is not reliable, reading data packets represented by an unreliable index segment from the storage medium 110, and/or extracting logical identifiers associated with data packets represented by an unreliable index segment from the data packets.
When writing entries to the forward map, indexing module 120 may write the forward map entries based on the sequence identifiers of the index segments. In other words, the indexing module 120 processes the index segments in sequential order following the sequence such that the forward map is properly populated and modified to reflect the operations recorded in the log-based structure stored on the storage media. Advantageously, this is accomplished without reading and processing each data packet in the logical erase block.
A means for recording, on the storage medium 110, information indicating where an index segment is written on the storage medium, in various embodiments, may include a storage controller 104, an indexing module 120, a write agent 404, a storage controller 506, a hardware controller 520, a device driver installed for the storage device 102 on the host computing system 114, other logic hardware, and/or other executable code stored on a computer readable storage medium. Other embodiments may include similar or equivalent means for recording information indicating where an index segment is written on the storage medium.
In some cases, a forward map entry may later be displaced by a subsequent forward map entry. For example, two data packets may comprise different data in relation one another, but may be associated with the same logical identifier. This situation may arise when data is written to a logical block address and later the data of the logical block address is modified (i.e., one data packet updates or modifies the data of the other data packet). Indexing module 120 may process a first index segment in the sequence (e.g., index segment 650a) and may write a forward map entry associated with the first of the two data packets to be written to the log-based structure to the forward map. Subsequently, indexing module 120 may process a second index segment to modify the forward map entry in the forward map associated with the first data packet to reflect the physical storage location of the second data packet. Accordingly, the forward map will retain the entry of the most recent data packet associated with the logical identifier as long as indexing module 120 makes forward map entries to the forward map according to an order in which data packets are written to solid-state storage media 110. To enforce the order, indexing module 120 may rely on the sequence identifiers of the index segments.

## Claims

1. A method comprising:
writing a plurality of data packets to a storage medium by sequentially appending the data packets to an append point of a log-based structure of the storage medium, the data packets associated with different logical identifiers belonging to a logical address space that is independent of physical storage locations on the storage medium;
writing an index segment associated with the plurality of data packets to the append point of the log-based structure, the index segment comprising index entries for determining the logical identifiers of the data packets; and
recording information on the storage medium, the information indicating where the index segment is written on the storage medium.

2. The method of claim 1 further comprising:
reading the index segment from the storage medium to build a forward map that maps the logical identifiers to physical locations of the data packets on the storage medium;
deriving physical addresses of the storage medium for the data packets from location information of the index segment; and
deriving the logical identifiers associated with the data packets from the index segment.

3. The method of claim 1 further comprising:
determining that the written index segment is not reliable;
reading the data packets represented by the unreliable index segment from the storage medium; and
extracting the logical identifiers associated with the data packets represented by the unreliable index segment from the data packets represented by the unreliable index segment.

4. The method of claim 1 wherein writing the index segment comprises writing the index segment to the log-based structure after writing the plurality of data packets to the log-based structure.

5. The method of claim 1 wherein the storage medium comprises a solid-state storage medium, and wherein writing the plurality of data packets comprises writing the plurality of data packets to a logical erase block, and writing the index segment comprises writing the index segment to the same logical erase block.

6. The method of claim 5 further comprising writing additional data packets to the logical erase block and ensuring that each additional data packet written to the logical erase block is indexed by an additional index segment also written to the logical erase block.

7. The method of claim 6 wherein the index segments represent different numbers of data packets.

8. The method of claim 1 further comprising writing additional data packets and additional index segments to the log-based structure and associating the index segments into one or more groups, each group comprising a different subset of the index segments.

9. The method of claim 8 wherein writing the data packets and the index segments comprises writing the data packets in a logical erase block and writing the index segments in the same logical erase block and wherein recording the information comprises writing an index root in a predetermined location of the same logical erase block, the index root pointing to at least one index segment of each group, the information comprising the index root.

10. The method of claim 9 wherein writing the index root comprises writing the index root to a position in the log-based structure that is subsequent to positions of the index segments in the log-based structure.

11. The method of claim 1 wherein the index segment comprises a pointer to another index segment stored in the same logical erase block as the index segment.

12. The method of claim 1 wherein at least one of the index entries comprises identifier information representing a plurality of the logical identifiers.

13. The method of claim 12 wherein the logical identifiers of the plurality are contiguous and are associated with an extent of data packets.

14. The method of claim 1 wherein sequentially appending the data packets to the log-based structure comprises writing the data packets sequentially to the storage medium such that an ordered sequence of storage operations completed on the storage medium is preserved on the storage medium.

15. The method of claim 1 further comprising accumulating the index entries until the index segment is a predetermined size prior to the writing of the index segment.

16. An apparatus comprising:
a storage controller configured to write a plurality of data packets to a storage medium by sequentially appending the data packets to one or more append points of one or more log-based structures of the storage medium, the data packets associated with different logical identifiers belonging to a logical address space that is independent of physical storage locations on the storage medium;
an indexing module configured to:
write index segments to one or more of the append points of the one or more log-based structures, each index segment associated with at least two of the data packets and the index segments comprising index entries for determining a storage operation context for the data packets;
preserve an order in which the index segments are written; and
identify locations of the index segments in the log-based structure from one or more pointers stored in predetermined locations of the storage medium.

17. The apparatus of claim 16 wherein the storage operation context for the data packets comprises location information describing physical addresses of the storage medium storing the data packets and identifier information describing the logical identifiers associated with the data packets.

18. The apparatus of claim 16 wherein:
the indexing module writes the data packets and the index segments to the same logical erase block of the storage medium;
the last index segment written to a logical erase block has a different size than the other index segments written to the logical erase block;
the last index segment written to the logical erase block is written earlier in the log-based structure than any data packets associated with the last index segment; and
the index segments written prior to the last index segment are written later in the log-based structure than their associated data packets.

19. An apparatus comprising:
means for writing a plurality of data packets to a storage medium by sequentially appending the data packets to an append point of a log-based structure of the storage medium, the data packets associated with different logical identifiers belonging to a logical address space that is independent of physical storage locations on the storage medium; and
means for writing an index segment associated with the plurality of data packets to the append point of the log-based structure, the index segment comprising index entries for determining the logical identifiers of the data packets and a sequence number identifying a sequence in which the index segment is written to the log-based structure; and
means for recording an index root on the storage medium, the index root comprising a pointer indicating where the index segment is written on the storage medium.

20. The apparatus of claim 19, further comprising:
means for reading one or more index segments from the storage medium to build a forward map that maps the logical identifiers to physical locations of the data packets on the storage medium;
means for deriving physical addresses of the storage medium for the data packets from location information of the one or more index segments; and
means for deriving the logical identifiers associated with the data packets from the one or more index segments.

21. The apparatus of claim 19, further comprising:
means for determining that a written index segment is not reliable;
means for reading the data packets represented by the unreliable index segment from the storage medium; and
means for extracting the logical identifiers associated with the data packets represented by the unreliable index segment from the data packets represented by the unreliable index segment.

22. The apparatus of claim 19 wherein the means for writing an index segment writes the index segment to the log-based structure after the plurality of data packets are written to the log-based structure.

23. A computer program product comprising a non-transitory computer readable medium having computer usable program code executable to perform operations, the operations of the computer program product comprising:
writing a plurality of data packets to a storage medium by sequentially appending the data packets to an append point of a log-based structure of the storage medium, the data packets associated with different logical identifiers belonging to a logical address space that is independent of physical storage locations on the storage medium;
writing index segments to the append point of the log-based structure, each index segment associated with an equal number of the data packets, and the index segments comprising index entries for determining the logical identifiers of the data packets; and
recording an indexing root on the storage medium, the indexing root comprising one or more pointers indicating where each index segment is written on the storage medium.

24. The computer program product of claim 23, the operations of the computer program product further comprising:
reading one or more index segments from the storage medium to build a forward map that maps the logical identifiers to physical locations of the data packets on the storage medium;
deriving physical addresses of the storage medium for the data packets from location information of the one or more index segments; and
deriving the logical identifiers associated with the data packets from the one or more index segments.

25. The computer program product of claim 23, the operations of the computer program product further comprising:
determining that a written index segment is not reliable;
reading the data packets represented by the unreliable index segment from the storage medium; and
extracting the logical identifiers associated with the data packets represented by the unreliable index segment from the data packets represented by the unreliable index segment.