Patent Publication Number: US-2023137039-A1

Title: Reduce Command Latency Using Block Pre-Erase

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     Embodiments of the present disclosure generally relate to a controller for a storage device, and more particularly to providing block-erase functionality to a storage device. 
     Description of the Related Art 
     Non-volatile memory (NVM) in a solid-state storage device such as a solid-state drive (SSD) conventionally requires erasing NVM memory blocks immediately prior to being programmed with useful data. NVM memory blocks marked as ready to receive new data are typically processed with a ‘flash and fill’ operation to hold placeholder data that needs to be erased before programming with the useful data. Before programming, these blocks must be physically erased. 
     A physical erase is a very long operation slowing down performance of the SSD at a point in time when write operations are pending. Moreover, for each physical erase, a program erase counter (PEC) for the erased block is incremented, shortening the useful life of the NVM. 
     Accordingly, what is needed are systems and methods to address the performance issues of conventional approaches. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure generally relates to system and apparatus for secure NVM format by pre-erase. According to certain embodiments when an NVM goes into idle mode, one or more free blocks are serially popped from a free block heap. The free block is then physically erased in an SLC mode, and then pushed to a pre-erase heap. The process is performed in both SLC and TLC partitions, in the TLC partition the block becomes HSLC (Hybrid SLC). This process increases a PEC value of the block, maintaining device longevity (the counter of erase operations of the current block). When there is a need to use a new block, it is popped from the pre-erase heap. In some cases where is a need to use a TLC block instead of HSLC, a special erase operation is taken which converts the block from HSLC to TLC, but doesn&#39;t increase a PEC value of the block. 
     In one embodiment, a data storage device is disclosed that includes a non-volatile memory (NVM) device, and a controller coupled to the NVM device and configured to perform a method for block pre-erase. The method includes, responsive to the NVM device being in an idle state, identifying a free block in a free block heap, erasing data in the free block to create an erased block, and adding the erased block to a pre-erase block list. 
     In another embodiment, a controller for a data storage device is disclosed, that includes a memory comprising computer-readable instructions, and a processor coupled to the memory and configured to read the computer-readable instructions. The computer-readable instructions cause the processor to erase data from a block of memory from an NVM device to generate an erased block, and add the erased block to a pre-erase block list. The computer-readable instructions further cause the processor to receive an erase command for a block of an NVM device, and responsive to receiving the erase command, provide the erased block from the pre-erase block list. 
     In another embodiment, a data storage device is disclosed that includes a non-volatile memory (NVM) means, and a controller configured to detect an idle state of the NVM means, identify a free block in a free block list, and erase data in the free block, thereby generating an erased block. The controller is further configured to provide the erased block to a pre-erase block list. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG.  1    is a schematic block diagram illustrating a storage system, according to certain embodiments. 
         FIG.  2    depicts a process diagram for NVM block pre-erase, according to certain embodiments. 
         FIG.  3    depicts a flow diagram depicting a secure NVM format process flow, according to certain embodiments. 
         FIG.  4    depicts an example method for secure format NVM by pre-erase, according to certain embodiments. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments, and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein, and shall not be considered an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     The present disclosure relates to a system and apparatus for secure NVM format by pre-erase. According to certain embodiments when an NVM does into idle mode, one or more free blocks are serially popped from a free block heap. The popped free block is converted to SLC mode if the block is not already in SLC mode by the following erase operation. The free block is then physically erased in an SLC mode, and then pushed to a pre-erase heap. When an erased block is needed in response to commands issued by a host (usually write commands), a block is popped from the pre-erase heap in response and is ready for usage. By using a pre-erased block from the pre-erase heap, latency of execution of the host command is reduced, as an erase operation is not needed at time of execution. 
     Example System 
       FIG.  1    is a schematic block diagram illustrating a storage system  100  in which a host device  104  is in communication with a data storage device (DSD)  106 , according to certain embodiments. For instance, the host device  104  may utilize a non-volatile memory (NVM)  110  included in DSD  106  to store and retrieve data. The host device  104  comprises a host DRAM  138 . In some examples, the storage system  100  may include a plurality of storage devices, such as the DSD  106 , which may operate as a storage array. For instance, the storage system  100  may include a plurality of DSD  106  configured as a redundant array of inexpensive/independent disks (RAID) that collectively function as a mass storage device for the host device  104 . 
     The host device  104  may store and/or retrieve data to and/or from one or more storage devices, such as the DSD  106 . As illustrated in  FIG.  1   , the host device  104  may communicate with the DSD  106  via an interface  114 . The host device  104  may comprise any of a wide range of devices, including computer servers, network-attached storage (NAS) units, desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or other devices capable of sending or receiving data from a data storage device. 
     The DSD  106  includes a controller  108 , NVM  110 , a power supply  111 , volatile memory  112 , the interface  114 , and a write buffer  116 . In some examples, the DSD  106  may include additional components not shown in  FIG.  1    for the sake of clarity. For example, the DSD  106  may include a printed circuit board (PCB) to which components of the DSD  106  are mechanically attached and which includes electrically conductive traces that electrically interconnect components of the DSD  106  or the like. In some examples, the physical dimensions and connector configurations of the DSD  106  may conform to one or more standard form factors. Some example standard form factors include, but are not limited to, 3.5″ data storage device (e.g., an HDD or SSD), 2.5″ data storage device, 1.8″ data storage device, peripheral component interconnect (PCI), PCI-extended (PCI-X), PCI Express (PCIe) (e.g., PCIe ×1, ×4, ×8, ×16, PCIe Mini Card, MiniPCI, etc.). In some examples, the DSD  106  may be directly coupled (e.g., directly soldered or plugged into a connector) to a motherboard of the host device  104 , or may be located remotely from the host  104  and accessed via a network or bus (e.g., PCIe) via interface  114 . 
     Interface  114  may include one or both of a data bus for exchanging data with the host device  104  and a control bus for exchanging commands with the host device  104 . Interface  114  may operate in accordance with any suitable protocol. For example, the interface  114  may operate in accordance with one or more of the following protocols: advanced technology attachment (ATA) (e.g., serial-ATA (SATA) and parallel-ATA (PATA)), Fibre Channel Protocol (FCP), small computer system interface (SCSI), serially attached SCSI (SAS), PCI, and PCIe, non-volatile memory express (NVMe), OpenCAPI, GenZ, Cache Coherent Interface Accelerator (CCIX), Open Channel SSD (OCSSD), or the like. Interface  114  (e.g., the data bus, the control bus, or both) is electrically connected to the controller  108 , providing an electrical connection between the host device  104  and the controller  108 , allowing data to be exchanged between the host device  104  and the controller  108 . In some examples, the electrical connection of interface  114  may also permit the DSD  106  to receive power from the host device  104 . For example, as illustrated in  FIG.  1   , the power supply  111  may receive power from the host device  104  via interface  114 . 
     The NVM  110  may include a plurality of memory devices or memory units. NVM  110  may be configured to store and/or retrieve data. For instance, a memory unit of NVM  110  may receive data and a message from controller  108  that instructs the memory unit to store the data. Similarly, the memory unit may receive a message from controller  108  that instructs the memory unit to retrieve data. In some examples, each of the memory units may be referred to as a die. In some examples, the NVM  110  may include a plurality of dies (i.e., a plurality of memory units). In some examples, each memory unit may be configured to store relatively large amounts of data (e.g., 128 MB, 256 MB, 512 MB, 1 GB, 2 GB, 4 GB, 8 GB, 16 GB, 32 GB, 64 GB, 128 GB, 256 GB, 512 GB, 1 TB, etc.). 
     In some examples, each memory unit may include any type of non-volatile memory devices, such as flash memory devices, phase-change memory (PCM) devices, resistive random-access memory (ReRAM) devices, magneto-resistive random-access memory (MRAM) devices, ferroelectric random-access memory (F-RAM), holographic memory devices, and any other type of non-volatile memory devices. 
     The NVM  110  may comprise a plurality of flash memory devices or memory units. NVM Flash memory devices may include NAND or NOR-based flash memory devices and may store data based on a charge contained in a floating gate of a transistor for each flash memory cell. In NVM flash memory devices, the flash memory device may be divided into a plurality of dies, where each die of the plurality of dies includes a plurality of physical or logical blocks, which may be further divided into a plurality of pages. Each block of the plurality of blocks within a particular memory device may include a plurality of NVM cells. Rows of NVM cells may be electrically connected using a word line to define a page of a plurality of pages. Respective cells in each of the plurality of pages may be electrically connected to respective bit lines. Furthermore, NVM flash memory devices may be 2D or 3D devices and may be single level cell (SLC), multi-level cell (MLC), triple level cell (TLC), or quad level cell (QLC). The controller  108  may write data to and from NVM flash memory devices at the page level and erase data from NVM flash memory devices at the block level. 
     The DSD  106  includes a flash translation layer (FTL)  150 , for providing logical to physical address translation, garbage collection, wear leveling, error correction code (ECC), bad block management, in addition to other functions described herein. The FTL  150  is coupled to the NVM  110 , and is coupled directly or indirectly to the controller  108 . FTL  150  includes a free block heap  152  for storing references to free blocks within the NVM  110 , and a pre-erase block heap  154  for storing references to erased blocks that are available for programming, as discussed further below. Although these structures are referred to as a ‘heap,’ one of skill in the art will appreciate that any suitable architecture may be used to store these references, such as a list, an array, a stack, or other suitable structure. It is understood that terms such as ‘push’ and ‘pull’ in the context of a heap or other data structure as used herein refers to storage of a reference to a location on the NVM  110 . Such a reference may be logical or physical. 
     The power supply  111  may provide power to one or more components of the DSD  106 . When operating in a standard mode, the power supply  111  may provide power to one or more components using power provided by an external device, such as the host device  104 . For instance, the power supply  111  may provide power to the one or more components using power received from the host device  104  via interface  114 . In some examples, the power supply  111  may include one or more power storage components configured to provide power to the one or more components when operating in an idle or shutdown mode, such as where power ceases to be received from the external device, or is received at a lower rate. In this way, the power supply  111  may function as an onboard backup power source. Some examples of the one or more power storage components include, but are not limited to, capacitors, super-capacitors, batteries, and the like. In some examples, the amount of power that may be stored by the one or more power storage components may be a function of the cost and/or the size (e.g., area/volume) of the one or more power storage components. In other words, as the amount of power stored by the one or more power storage components increases, the cost and/or the size of the one or more power storage components also increases. 
     The volatile memory  112  may be used by controller  108  to store information such as command queues, error correction code (ECC) data, and other data that may be utilized by the controller  108  during operation of the DSD  106 . Volatile memory  112  may include one or more volatile memory devices. In some examples, controller  108  may use volatile memory  112  as a cache. For instance, controller  108  may store cached information in volatile memory  112  until the cached information is written to the NVM  110 . As illustrated in  FIG.  1   , volatile memory  112  may consume power received from the power supply  111 . Examples of volatile memory  112  include, but are not limited to, random-access memory (RAM), dynamic random access memory (DRAM), static RAM (SRAM), and synchronous dynamic RAM (SDRAM (e.g., DDR1, DDR2, DDR3, DDR3L, LPDDR3, DDR4, LPDDR4, and the like)). 
     Controller  108  may manage one or more operations of the DSD  106 . For instance, controller  108  may manage the reading of data from and/or the writing of data to the NVM  110 . In some embodiments, when the DSD  106  receives a write command from the host device  104 , the controller  108  may initiate a data storage command to store data to the NVM  110  and monitor the progress of the data storage command. Controller  108  may determine at least one operational characteristic of the storage system  100  and store at least one operational characteristic in the NVM  110 . In some embodiments, when the DSD  106  receives a write command from the host device  104 , the controller  108  temporarily stores the data associated with the write command in the internal memory or write buffer  116  before sending the data to the NVM  110 . Controller further includes a secure format NVM component  156  that causes the FTL  150  to execute a process for secure pre-erase of free blocks, discussed below. Controller  108  further includes a command synchronization (CS) FTL log  158  for storing synchronized commands such as the pre-erase command as discussed below, for recovery of the DSD  106  after an ungraceful shut down (UGSD), to recover a pre-erase heap (discussed below). 
     According to certain embodiments, when the DSD  106  enters an idle mode, the controller causes the FTL  150  to pop a free block from the free block heap  152  and perform an SLC erase on the free block, and moving the erased free block to the pre-erase block heap  154 . According to certain embodiments, if the free block is not already an SLC block, such as a TLC block, the block is converted to a hybrid SLC (HSLC) block (e.g., an SLC block in a TLC partition) and the erase is performed. According to certain embodiments, the erase is a physical erase, while in other the erase may be a logical erase, or a combination of a logical and physical erase. 
     When the host issues a command requiring an erased block, or erasure of a block, if there are erased blocks available in the pre-erase block heap  154 , these blocks are provided in response to the host command. If there are no blocks available in the pre-erase block heap  154 , a block is retrieved from the free block heap  152  and an erase is performed. By erasing free blocks during idle cycles of the DSD  106  and providing these via the pre-erase block heap  154 , when a host issues a command requiring an erased block, the long process of erasing a block (e.g., a physical erase) may be avoided, thereby improving performance of the DSD  106 . 
     Example Process Diagram 
       FIG.  2    depicts a process diagram  200  for NVM block pre-erase, according to certain embodiments. At block  204 , the controller  108  detects that the DSD  106  is in an idle state. At block  208 , when controller  108  detects that the DSD  106  is in an idle state, the controller  108  causes the FTL  150  to iteratively pop free blocks off of the free block heap  152  and cause these free blocks to be securely (e.g., physically) erased. At block  212 , the FTL  150  stores the erased blocks in the pre-erase block heap  154 . According to certain embodiments, if the idle state is exited, the FTL  150  ceases popping off and erasing further free blocks until the DSD  106  enters an idle state once more. 
     At block  216 , an erase block command is received by the controller  108 , such as issued by the host  104 , for example, as part of a write command issued by the host  104 . According to certain embodiments, such a command may be one that requires an erased block for operation. At block  220 , instead of performing an erase on a block, an erased block is provided by popping an erased block from the pre-erase block heap  154 . According to certain embodiments, the controller  108  may cause the erased block to be popped from the pre-erase block heap  154 , while in other embodiments, the FTL  150  may cause the erased block to be popped in response to the command from the host. 
     Example Flow Diagram for Secure NVM Format 
       FIG.  3    depicts a flow diagram  300  depicting a secure NVM format process flow, according to certain embodiments. According to certain embodiments, pre-erase blocks added to the pre-erase block heap in accordance with the process of  FIG.  2    may be utilized to increase performance (e.g., decrease latency) of a secure NVM format, executed by secure NVM format component  156 . 
     At block  304 , the controller  108  with secure format NVM component  156  configured to utilize pre-erase blocks in the pre-erase block heap  154  resulting from the process depicted by  FIG.  2   . 
     At block  304 , one or more un-erased blocks are popped from the free block heap  152 , erased, and pushed to the pre-erase block heap  154 , similar to the process depicted in  FIG.  2   . At block  308 , un-erased blocks are popped from the free block heap  152 , the blocks are erased (e.g., physically erased) and pushed to the pre-erase block heap  154 , similar to the process depicted in  FIG.  2   . 
     At block  312 , a secure NVM format command is received by the controller. In executing the secure NVM format command, the secure NVM format component  156  skips erase operation for blocks that are listed in the pre-erase block heap  154 ,  156 . 
     At block  316 , the secure format NVM component  156  execution is synchronized with the command synch flow, and the pre-erase block heap  154  is stored in the CS FTL log  158 . At block  320 , the pre-erase block heap  154  may be recovered from the CS FTL log  158 . 
     Example Method 
       FIG.  4    depicts an example method  400  for secure format NVM by pre-erase, according to certain embodiments. According to certain embodiments, a block of memory from an NVM device such as NVM  110  is pushed to the pre-erase block heap  154 , and the controller  108  detects an idle state of one or more components of the DSD  106 , such as the NVM device. 
     At block  404 , the controller  108  erases data from a block of memory of an NVM device, such as NVM  110 , to generate an erased block. According to certain embodiments, the erase is an SLC erase. If the block is configured to be of a different cell type, such as TLC, the block is first converted to SLC. 
     At block  408 , the FTL  150  pushes the erased block to the pre-erase block heap  154 . According to certain embodiments, the erased block is maintained in an erased state while stored in the pre-erase heap. 
     At block  412 , the DSD  106  receives an erase command from the host  104 , for a block of the NVM device. 
     At block  416 , responsive to receiving the erase command, the FTL  150  provides the erased block from the pre-erase block heap  154 . According to certain embodiments, the erased block may be provided in response to a write command. 
     Additional Considerations 
     The preceding description is provided to enable any person skilled in the art to practice the various embodiments described herein. The examples discussed herein are not limiting of the scope, applicability, or embodiments set forth in the claims. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments. For example, changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to some examples may be combined in some other examples. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method that is practiced using other structure, functionality, or structure and functionality in addition to, or other than, the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim. 
     As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. 
     As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c). 
     As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. 
     The methods disclosed herein comprise one or more steps or actions for achieving the methods. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. Further, the various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. 
     The following claims are not intended to be limited to the embodiments shown herein, but are to be accorded the full scope consistent with the language of the claims. Within a claim, reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. 
     In one embodiment, a data storage device is disclosed that includes a non-volatile memory (NVM) device, and a controller coupled to the NVM device and configured to perform a method for NVM pre-erase. The method includes, responsive to the NVM device being in an idle state, identifying a free block in a free block heap, erasing data in the free block to create an erased block, and adding the erased block to a pre-erase block list. According to certain embodiments, the method further includes, responsive to an erase command received from a host, popping the erased block from the pre-erase block heap. In certain embodiments, erasing the data includes an SLC erase, and erasing the data may further include converting a TLC to an SLC and then performing the SLC erase. The method further includes maintaining the erased block in an erased state. According to certain embodiments, the pre-erase block heap is stored in an FTL of the controller. In some embodiments, the method further includes updating the pre-erase block heap upon popping the erased block from the pre-erase block heap, responsive to a write command. 
     In another embodiment, a controller for a data storage device is disclosed, that includes a memory comprising computer-readable instructions, and a processor coupled to the memory and configured to read the computer-readable instructions. The computer-readable instructions cause the processor to erase data from a block of memory from an NVM device to generate an erased block, and add the erased block to a pre-erase block list. The computer-readable instructions further cause the processor to receive an erase command for a block of an NVM device, and responsive to receiving the erase command, provide the erased block from the pre-erase block list. The computer-readable instructions further cause the processor to allocate the block of memory to a free-block heap, and identify an idle state of the NVM device, and responsive to identification of the idle state of the NVM device, erasing data from the block of memory. The computer-readable instructions that cause the processor to erase data from the block of memory includes an SLC erase. The computer-readable instructions that cause the processor to erase data from the block of memory includes converting a TLC to an SLC and performing the SLC erase. The computer-readable instructions further cause the processor to maintain the erased block in an erased state. The controller further includes an FTL, wherein the pre-erase block heap is stored in the FTL. The computer-readable instructions further cause the processor to update the pre-erase block heap upon popping the erased block from the pre-erase block heap, responsive to a write command. 
     In another embodiment, a data storage device is disclosed that includes a non-volatile memory (NVM) means, and a controller configured to detect an idle state of the NVM means, identify a free block in a free block list, and erase data in the free block, thereby generating an erased block. The controller is further configured to provide the erased block to a pre-erase block list. The controller is further configured to receive an erase command and responsive to the erase command, pop the erased block from the pre-erase block heap. The controller is further configured to erase data in the free block with an SLC erase. The controller is further configured to maintain the erased block in an erased state. The controller is further configured to store the pre-erase block heap in a FTL means. The controller is further configured to update the pre-erase block heap upon an allocation of the erased block in response to a command from a host. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.