Patent Grant
9817752
The disclosed embodiments relate generally to memory systems, and in particular, to enhancing data integrity of a storage system (e.g., comprising one or more flash memory devices) to protect against returning old versions of data.
Semiconductor memory devices, including flash memory, typically utilize memory cells to store data as an electrical value, such as an electrical charge or voltage. A flash memory cell, for example, includes a single transistor with a floating gate that is used to store a charge representative of a data value. Flash memory is a non-volatile data storage device that can be electrically erased and reprogrammed. More generally, non-volatile memory (e.g., flash memory, as well as other types of non-volatile memory implemented using any of a variety of technologies) retains stored information even when not powered, as opposed to volatile memory, which requires power to maintain the stored information. Increases in storage density have been facilitated in various ways, including increasing the density of memory cells on a chip enabled by manufacturing developments, and transitioning from single-level flash memory cells to multi-level flash memory cells, so that two or more bits can be stored by each flash memory cell.
Data integrity warrants maintaining and assuring accuracy and consistency of data, and is critical to systems that store, process, and/or retrieve data. Any unintended changes to data as the result of a storage, retrieval or processing operation (e.g., due to unexpected hardware failure) is failure of data integrity. Some data integrity mechanisms (e.g., ECC) protect data against common kinds of internal data corruption, such as undetected bit-flips in memory. However, it is also important for data integrity mechanisms to protect against data integrity failures across longer data paths (e.g., from a data storage device to a host system).
Various embodiments of systems, methods and devices within the scope of the appended claims each have several aspects, no single one of which is solely responsible for the attributes described herein. Without limiting the scope of the appended claims, after considering this disclosure, and particularly after considering the section entitled “Detailed Description” one will understand how the aspects of various embodiments are used to enable enhancing data integrity to protect against returning old versions of data. In one aspect, for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by a write request from a host, one or more operations are performed, including (1) generating metadata for the subset, the metadata including a version number for the subset, (2) calculating a first Cyclic Redundancy Check (CRC) checksum for the subset, and (3) storing the version number for the subset and the first CRC checksum for the subset in a version data structure.
So that the present disclosure can be understood in greater detail, a more particular description may be had by reference to the features of various embodiments, some of which are illustrated in the appended drawings. The appended drawings, however, merely illustrate pertinent features of the present disclosure and are therefore not to be considered limiting, for the description may admit to other effective features.
In accordance with common practice the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures.
The various embodiments described herein include systems, methods and/or devices used to enable enhancing data integrity to protect against returning old versions of data. Some embodiments include systems, methods and/or devices to perform, for each logical block specified by a write request from a host, one or more operations, including (1) generating metadata for the logical block, the metadata including a version number, (2) storing the metadata, including the version number, for the logical block in a header of a physical page in which the logical block is stored, and (3) storing the version number for the logical block in a version data structure.
(A1) More specifically, some embodiments include a method of enhancing data integrity. In some embodiments, the method includes (1) receiving, at a storage device, a write request from a host, wherein the write request specifies write data for a first set of one or more logical block addresses in a logical address space of the host, (2) mapping, using a mapping table, the first set of one or more logical block addresses associated with the write request to a first set of one or more physical addresses of the storage device, the first set of one or more physical addresses corresponding to one or more physical pages of the storage device, and (3) performing one or more operations for each logical block specified by the first set of one or more logical block addresses, including: (a) generating metadata for the logical block, the metadata including a version number for the logical block, (b) storing the metadata, including the version number, for the logical block in a header of a physical page in which the logical block is stored, and (c) storing the version number for the logical block in a version data structure.
(A2) In some embodiments of the method of A1, performing one or more operations for each logical block specified by the first set of one or more logical block addresses further comprises, in accordance with a determination that the logical block is modified, (1) obtaining an updated version number for the logical block, (2) mapping, using the mapping table, the logical block to a new physical page of the storage device, (3) storing the updated version number for the logical block in a header of the new physical page in which the logical block is stored, and (4) storing the updated version number for the logical block in the version data structure.
(A3) In some embodiments of the method of A2, obtaining an updated version number for the logical block comprises (1) reading the version number for the logical block from the version data structure, and (2) incrementing the version number for the logical block.
(A4) In some embodiments of the method of any of A1 to A3, the method further includes (1) receiving, at the storage device, a read request from the host, wherein the read request specifies a second set of one or more logical block addresses in the logical address space of the host from which to read, (2) mapping, using the mapping table, the second set of one or more logical block addresses associated with the read request to a second set of one or more physical addresses corresponding to one or more physical pages of the storage device, (3) performing one or more operations for each logical block specified by the second set of one or more logical block addresses, including (a) reading the version number for the logical block from the version data structure, (b) reading the version number for the logical block from the header of the physical page in which the logical block is stored, (c) comparing the version number from the version data structure with the version number from the header of the physical page, and (d) in accordance with a determination that the version number from the version data structure is not equivalent to the version number from the header of the physical page, initiating one or more recovery actions, and (4) in accordance with a determination that, for all the logical blocks specified by the second set of one or more logical block addresses, the version number from the version data structure is equivalent to the version number from the header of the physical page, returning data read from the second set of one or more logical block addresses to the host.
(A5) In some embodiments of the method of any of A1 to A4, the mapping table is stored independently from the version data structure.
(A6) In some embodiments of the method of any of A1 to A5, the metadata for the logical block includes a checksum from a Cyclic Redundancy Check (CRC) operation.
(A7) In some embodiments of the method of any of A1 to A6, the metadata for the logical block includes an identification value.
(A8) In some embodiments of the method of any of A1 to A7, the metadata for the logical block includes an application tag.
(A9) In some embodiments of the method of any of A1 to A8, the metadata for the logical block includes a reference tag.
(A10) In some embodiments of the method of any of A1 to A9, the storage device comprises one or more flash memory devices.
(A11) In another aspect, a storage device includes a storage medium, memory distinct from the storage medium, the memory storing a mapping table, the mapping table including information for mapping logical addresses in a logic address space of a host to physical addresses in a physical address space of the storage system, and a storage controller having one or more processors configured to execute instructions in one or more programs, wherein the storage controller is configured to perform or control performance of any of the methods A1 to A10 described herein.
(A12) In some embodiments of the storage device of A11, the storage controller includes a version module for generating the version number for the logical block and storing the version number for the logical block in the version data structure, and a recovery module for initiating one or more recovery actions in accordance with a determination that a version number obtained from the version data structure is not equivalent to a version number obtained from a header of a respective physical page in the storage medium.
(A13) In yet another aspect, any of the methods A1 to A10 described above are performed by a storage device including means for performing any of the methods described herein.
(A14) In yet another aspect, a storage system includes (1) a storage medium (e.g., comprising one or more non-volatile storage devices, such as flash memory devices) (2) one or more processors, and (3) memory (e.g., non-volatile memory or volatile memory in the storage system) storing one or more programs, which when executed by the one or more processors cause the storage system to perform or control performance of any of the methods A1 to A10 described herein.
(A15) In yet another aspect, some embodiments include a non-transitory computer readable storage medium, storing one or more programs configured for execution by one or more processors of a storage device, the one or more programs including instructions for performing any of the methods described herein.
The various embodiments described herein include systems, methods and/or devices used to enable enhancing data integrity to protect against returning old versions of data. Some embodiments include systems, methods and/or devices to perform, for each subset of a mapping table that includes at least one entry corresponding to a logical block specified by a write request from a host, one or more operations, including (1) generating metadata for the subset, the metadata including a version number for the subset, (2) calculating a first Cyclic Redundancy Check (CRC) checksum for the subset, and (3) storing the version number for the subset and the first CRC checksum for the subset in a version data structure.
(B1) More specifically, some embodiments include a method of enhancing data integrity. In some embodiments, the method includes (1) receiving, at a storage device, a write request from a host, wherein the write request specifies write data for a first set of one or more logical block addresses in a logical address space of the host, (2) mapping, using a mapping table, the first set of one or more logical block addresses associated with the write request to a first set of one or more physical addresses of the storage device, wherein the mapping table includes a plurality of subsets, each subset having entries corresponding to a group of contiguous logical blocks in the logical address space of the host, and (3) performing one or more operations for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the first set of one or more logical block addresses, including: (a) generating metadata for the subset, the metadata including a version number for the subset, (b) calculating a first Cyclic Redundancy Check (CRC) checksum for the subset, and (c) storing the version number for the subset and the first CRC checksum for the subset in a version data structure.
(B2) In some embodiments of the method of B1, performing one or more operations for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the first set of one or more logical block addresses further comprises, in accordance with a determination that at least one entry of the subset is modified, (1) obtaining an updated version number for the subset, (2) calculating an updated CRC checksum for the subset, and (3) storing the updated version number for the subset and the updated CRC checksum for the subset in the version data structure.
(B3) In some embodiments of the method of B2, obtaining an updated version number for the subset comprises (1) reading the version number for the subset from the version data structure, and (2) incrementing the version number for the subset.
(B4) In some embodiments of the method of any of B1 to B3, the method further includes (1) receiving, at the storage device, a read request from the host, wherein the read request specifies a second set of one or more logical block addresses in the logical address space of the host from which to read, (2) mapping, using the mapping table, the second set of one or more logical block addresses associated with the read request to a second set of one or more physical addresses corresponding to one or more physical pages of the storage device, (3) performing one or more operations for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the second set of one or more logical block addresses, including: (a) reading the first CRC checksum for the subset from the version data structure, (b) calculating a second CRC checksum for the subset, (c) comparing the second CRC checksum for the subset with the first CRC checksum for the subset, and (d) in accordance with a determination that the second CRC checksum is not equivalent to the first CRC checksum, initiating one or more recovery actions, and (4) in accordance with a determination that, for all the subsets that include at least one entry corresponding to a logical block specified by the second set of one or more logical block addresses, the second CRC checksum is equivalent to the first CRC checksum, returning data from the second set of one or more logical block addresses to the host.
(B5) In some embodiments of the method of any of B1 to B4, the mapping table is stored independently from the version data structure.
(B6) In some embodiments of the method of any of B1 to B5, the storage device comprises one or more flash memory devices.
(B7) In another aspect, a storage device includes a storage medium, memory distinct from the storage medium, the memory storing a mapping table, the mapping table including information for mapping logical addresses in a logic address space of a host to physical addresses in a physical address space of the storage system, and a storage controller having one or more processors configured to execute instructions in one or more programs, wherein the storage controller is configured to perform or control performance of any of the methods B1 to B6 described herein.
(B8) In some embodiments of the storage device of B7, the storage controller includes a version module and a CRC module for generating the version number for the subset and the first CRC checksum for the subset, and for storing the version number for the subset and the first CRC checksum for the subset in the version data structure.
(B9) In yet another aspect, any of the methods B1 to B6 described above are performed by a storage device including means for performing any of the methods described herein.
(B10) In yet another aspect, a storage system includes (1) a storage medium (e.g., comprising one or more non-volatile storage devices, such as flash memory devices) (2) one or more processors, and (3) memory (e.g., non-volatile memory or volatile memory in the storage system) storing one or more programs, which when executed by the one or more processors cause the storage system to perform or control performance of any of the methods B1 to B6 described herein.
(B11) In yet another aspect, some embodiments include a non-transitory computer readable storage medium, storing one or more programs configured for execution by one or more processors of a storage device, the one or more programs including instructions for performing any of the methods B1 to B6 described herein.
Numerous details are described herein in order to provide a thorough understanding of the example embodiments illustrated in the accompanying drawings. However, some embodiments may be practiced without many of the specific details, and the scope of the claims is only limited by those features and aspects specifically recited in the claims. Furthermore, well-known methods, components, and circuits have not been described in exhaustive detail so as not to unnecessarily obscure more pertinent aspects of the embodiments described herein.
Computer system 110 is coupled to storage controller 124 through data connections 101. However, in some embodiments computer system 110 includes storage controller 124, or a portion of storage controller 124, as a component and/or a subsystem. For example, in some embodiments, some or all of the functionality of storage controller 124 is implemented by software executed on computer system 110. Computer system 110 may be any suitable computer device, such as a computer, a laptop computer, a tablet device, a netbook, an internet kiosk, a personal digital assistant, a mobile phone, a smart phone, a gaming device, a computer server, or any other computing device. Computer system 110 is sometimes called a host, host system, client, or client system. In some embodiments, computer system 110 is a server system, such as a server system in a data center. In some embodiments, computer system 110 includes one or more processors, one or more types of memory, a display and/or other user interface components such as a keyboard, a touch screen display, a mouse, a track-pad, a digital camera and/or any number of supplemental devices to add functionality. In some embodiments, computer system 110 does not have a display and other user interface components.
Storage medium 130 is coupled to storage controller 124 through connections 103. Connections 103 are sometimes called data connections, but typically convey commands in addition to data, and optionally convey metadata, error correction information and/or other information in addition to data values to be stored in storage medium 130 and data values read from storage medium 130. In some embodiments, however, storage controller 124 and storage medium 130 are included in the same device (i.e., an integral device) as components thereof. Furthermore, in some embodiments, storage controller 124 and storage medium 130 are embedded in a host device (e.g., computer system 110), such as a mobile device, tablet, other computer or computer controlled device, and the methods described herein are performed, at least in part, by the embedded memory controller. Storage medium 130 may include any number (i.e., one or more) of memory devices including, without limitation, non-volatile semiconductor memory devices, such as flash memory device(s). For example, flash memory device(s) can be configured for enterprise storage suitable for applications such as cloud computing, for database applications, primary and/or secondary storage, or for caching data stored (or to be stored) in secondary storage, such as hard disk drives. Additionally and/or alternatively, flash memory device(s) can also be configured for relatively smaller-scale applications such as personal flash drives or hard-disk replacements for personal, laptop, and tablet computers.
Storage medium 130 is divided into a number of addressable and individually selectable blocks, such as selectable portion 131. In some embodiments, the individually selectable blocks are the minimum size erasable units in a flash memory device. In other words, each block contains the minimum number of memory cells that can be erased simultaneously. Each block is usually further divided into a plurality of pages and/or word lines, where each page or word line is typically an instance of the smallest individually accessible (readable) portion in a block. In some embodiments (e.g., using some types of flash memory), the smallest individually accessible unit of a data set, however, is a sector, which is a subunit of a page. That is, a block includes a plurality of pages, each page contains a plurality of sectors, and each sector is the minimum unit of data for reading data from the flash memory device.
As noted above, while data storage densities of non-volatile semiconductor memory devices are generally increasing, a drawback of increasing storage density is that the stored data is more prone to being stored and/or read erroneously. In some embodiments, error control coding can be utilized to limit the number of uncorrectable errors that are introduced by electrical fluctuations, defects in the storage medium, operating conditions, device history, write-read circuitry, etc., or a combination of these and various other factors.
In some embodiments, storage controller 124 includes a management module 121-1 (or management module 121-1-A, shown in more detail in
In some embodiments, management module 121-1 includes one or more processing units (CPUs, also sometimes called processors) 122-1 configured to execute instructions in one or more programs (e.g., in management module 121-1). In some embodiments, the one or more CPUs 122-1 are shared by one or more components within, and in some cases, beyond the function of storage controller 124. Management module 121-1 is coupled to host interface 129, additional module(s) 125 and storage medium I/O 128 in order to coordinate the operation of these components. In some embodiments, one or more modules of management module 121-1 are implemented in management module 121-2 of computer system 110. In some embodiments, one or more processors of computer system 110 (not shown) are configured to execute instructions in one or more programs (e.g., in management module 121-2). Management module 121-2 is coupled to storage device 120 in order to manage the operation of storage device 120.
Additional module(s) 125 are coupled to storage medium I/O 128, host interface 129, and management module 121-1. As an example, additional module(s) 125 may include an error control module to limit the number of uncorrectable errors inadvertently introduced into data during writes to memory or reads from memory. In some embodiments, additional module(s) 125 are executed in software by the one or more CPUs 122-1 of management module 121-1, and, in other embodiments, additional module(s) 125 are implemented in whole or in part using special purpose circuitry (e.g., to perform encoding and decoding functions). In some embodiments, additional module(s) 125 are implemented in whole or in part by software executed on computer system 110.
In some embodiments, an error control module, included in additional module(s) 125, includes an encoder and a decoder. In some embodiments, the encoder encodes data by applying an error control code to produce a codeword, which is subsequently stored in storage medium 130. When the encoded data (e.g., one or more codewords) is read from storage medium 130, the decoder applies a decoding process to the encoded data to recover the data, and to correct errors in the recovered data within the error correcting capability of the error control code. Those skilled in the art will appreciate that various error control codes have different error detection and correction capacities, and that particular codes are selected for various applications for reasons beyond the scope of this disclosure. As such, an exhaustive review of the various types of error control codes is not provided herein. Moreover, those skilled in the art will appreciate that each type or family of error control codes may have encoding and decoding algorithms that are particular to the type or family of error control codes. On the other hand, some algorithms may be utilized at least to some extent in the decoding of a number of different types or families of error control codes. As such, for the sake of brevity, an exhaustive description of the various types of encoding and decoding algorithms generally available and known to those skilled in the art is not provided herein.
In some embodiments, during a write operation, host interface 129 receives data to be stored in storage medium 130 from computer system 110. The data received by host interface 129 is made available to an encoder (e.g., in additional module(s) 125), which encodes the data to produce one or more codewords. The one or more codewords are made available to storage medium I/O 128, which transfers the one or more codewords to storage medium 130 in a manner dependent on the type of storage medium being utilized.
In some embodiments, a read operation is initiated when computer system (host) 110 sends one or more host read commands (e.g., via data connections 101, or alternatively a separate control line or bus) to storage controller 124 requesting data from storage medium 130. Storage controller 124 sends one or more read access commands to storage medium 130, via storage medium I/O 128, to obtain raw read data in accordance with memory locations (addresses) specified by the one or more host read commands. Storage medium I/O 128 provides the raw read data (e.g., comprising one or more codewords) to a decoder (e.g., in additional module(s) 125). If the decoding is successful, the decoded data is provided to host interface 129, where the decoded data is made available to computer system 110. In some embodiments, if the decoding is not successful, storage controller 124 may resort to a number of remedial actions or provide an indication of an irresolvable error condition.
As explained above, a storage medium (e.g., storage medium 130) is divided into a number of addressable and individually selectable blocks and each block is optionally (but typically) further divided into a plurality of pages and/or word lines and/or sectors. While erasure of a storage medium is performed on a block basis, in many embodiments, reading and programming of the storage medium is performed on a smaller subunit of a block (e.g., on a page basis, word line basis, or sector basis). In some embodiments, the smaller subunit of a block consists of multiple memory cells (e.g., single-level cells or multi-level cells). In some embodiments, programming is performed on an entire page. In some embodiments, a multi-level cell (MLC) NAND flash typically has four possible states per cell, yielding two bits of information per cell. Further, in some embodiments, a MLC NAND has two page types: (1) a lower page (sometimes called fast page), and (2) an upper page (sometimes called slow page). In some embodiments, a triple-level cell (TLC) NAND flash has eight possible states per cell, yielding three bits of information per cell. Although the description herein uses TLC, MLC, and SLC as examples, those skilled in the art will appreciate that the embodiments described herein may be extended to memory cells that have more than eight possible states per cell, yielding more than three bits of information per cell.
The encoding format of the storage media (i.e., TLC, MLC, or SLC and/or a chose data redundancy mechanism) is a choice made when data is actually written to the storage media. Often in this specification there is described an event, condition, or process that is said to set the encoding format, alter the encoding format of the storage media, etc. It should be recognized that the actual process may involve multiple steps, e.g., erasure of the previous contents of the storage media followed by the data being written using the new encoding format and that these operations may be separated in time from the initiating event, condition or procedure.
As an example, if data is written to a storage medium in pages, but the storage medium is erased in blocks, pages in the storage medium may contain invalid (e.g., stale) data, but those pages cannot be overwritten until the whole block containing those pages is erased. In order to write to the pages with invalid data, the pages (if any) with valid data in that block are read and re-written to a new block and the old block is erased (or put on a queue for erasing). This process is called garbage collection. After garbage collection, the new block contains the pages with valid data and may have free pages that are available for new data to be written, and the old block can be erased so as to be available for new data to be written. Since flash memory can only be programmed and erased a limited number of times, the efficiency of the algorithm used to pick the next block(s) to re-write and erase has a significant impact on the lifetime and reliability of flash-based storage systems.
In some circumstances when erasure of invalid data is deferred (e.g., garbage collection is performed later as part of background operations), the risk is increased that the invalid data (e.g., an older version of the data) is accidentally accessed. Further, in some embodiments, in order to improve endurance of a storage device of a flash-based storage system, erasure of multiple blocks containing older versions of data are deferred for a long duration (e.g., until a predetermined threshold of free blocks has been reached). In testing, a failure to return the correct (e.g., current) version is called a version mis-comparison error. Although existing end-to-end data integrity mechanisms may protect data against the most common error scenarios such as data displacement and undetected bit-flips in memory, they fail to protect against transfer of older versions of data to a host. The various embodiments described herein include systems, methods and/or devices used to enable enhancing data integrity to protect against returning old versions of data.
Each of the above identified elements may be stored in one or more of the previously mentioned memory devices, and corresponds to a set of instructions for performing a function described above. The above identified modules or programs (i.e., sets of instructions) need not be implemented as separate software programs, procedures or modules, and thus various subsets of these modules may be combined or otherwise re-arranged in various embodiments. In some embodiments, memory 206 may store a subset of the modules and data structures identified above. Furthermore, memory 206 may store additional modules and data structures not described above. In some embodiments, the programs, modules, and data structures stored in memory 206, or the non-transitory computer readable storage medium of memory 206, provide instructions for implementing some of the methods described below. In some embodiments, some or all of these modules may be implemented with specialized hardware circuits that subsume part or all of the module functionality.
Although
Version data structure 244-i illustrates an implementation of a version data structure for a respective LBA (e.g., LBA m,
Each of the above identified elements may be stored in one or more of the previously mentioned memory devices, and corresponds to a set of instructions for performing a function described above. The above identified modules or programs (i.e., sets of instructions) need not be implemented as separate software programs, procedures or modules, and thus various subsets of these modules may be combined or otherwise re-arranged in various embodiments. In some embodiments, memory 206 may store a subset of the modules and data structures identified above. Furthermore, memory 206 may store additional modules and data structures not described above. In some embodiments, the programs, modules, and data structures stored in memory 206, or the non-transitory computer readable storage medium of memory 206, provide instructions for implementing some of the methods described below. In some embodiments, some or all of these modules may be implemented with specialized hardware circuits that subsume part or all of the module functionality.
Although
Version data structure 274-i illustrates an implementation of a version data structure for a respective subset (e.g., subset i) of a plurality of subsets of a mapping table (e.g., forward mapping table 302,
In some embodiments, forward mapping table 302 is used to translate a logical block address (LBA) from the perspective of a host (e.g., computer system 110,
In some embodiments, forward mapping table 302 is stored in memory associated with the storage device (e.g., in memory 206, as part of mapping table 222,
In some embodiments, a logical address space corresponds to a plurality of subsets in a mapping table (e.g., subset 1 through subset N), and each subset of the mapping table includes one or more LBAs. In some embodiments, a subset corresponds to a set of contiguous mapping entries in a mapping table. For example, in
In some embodiments, as described above with respect to
In some embodiments, as described above with respect to
A storage device (e.g., storage device 120,
In some embodiments, the storage device includes (416) one or more flash memory devices. In some embodiments, the storage device includes a storage medium (e.g., storage medium 130,
The storage device maps (404), using a mapping table (e.g., forward mapping table 302,
The storage device performs (406) one or more operations for each logical block specified by the first set of one or more logical block addresses, including: (1) generating (408) metadata for the logical block, the metadata including a version number for the logical block, (2) storing (410) the metadata, including the version number, for the logical block in a header of a physical page in which the logical block is stored, and (3) storing (412) the version number for the logical block in a version data structure. In some embodiments, a logical block module (e.g., logical block module 226,
In some embodiments, some (e.g., one, some, or all) of the operations performed for each logical block specified by the first set of one or more logical block addresses are performed at the storage device (e.g., storage device 120,
As noted above, the storage device generates (408) metadata for the logical block, the metadata including a version number for the logical block. In some embodiments, if the logical block is being written for the first time, the storage device generates metadata for the logical block, the metadata including an initial version number (e.g., version number 1) for the logical block. For example, if LBA m of logical address space 310 (
In some embodiments, the metadata for the logical block includes (422) a checksum from a Cyclic Redundancy Check (CRC) operation. In some embodiments, the metadata includes a CRC value corresponding to a checksum calculated from data that includes data for the logical block. Using the example of LBA m from above, in some embodiments, the metadata includes a CRC-16 checksum calculated on the data associated with LBA m.
In some embodiments, the metadata for the logical block includes (424) an identification value. In some embodiments, the identification value is the logical block address for the logical block. For example, for LBA 80, in some embodiments, the metadata for LBA 80 includes an identification value of 80.
In some embodiments, the metadata for the logical block includes (426) an application tag. In some embodiments, the application tag includes an opaque data field that is not interpreted by a controller (e.g., storage controller 124,
In some embodiments, the metadata for the logical block includes (428) a reference tag. In some embodiments, the reference tag for a given logical block is computed by adding the reference tag in the command context to the logical block offset of the given logical block. In some embodiments, the reference tag is 4 bytes long (e.g., per T10 Protection Information standards). In some embodiments, the reference tag protects against data displacement.
As mentioned above, the storage device stores (410) the metadata, including the version number, for the logical block in a header of a physical page in which the logical block is stored. For example, if LBA m (
As mentioned above, the storage device stores (412) the version number for the logical block in a version data structure. Using the example of LBA m from above, the storage devices stores the version number (e.g., version number 1) for LBA m in a version data structure (e.g., in version number 246 of version data structure 244 corresponding to LBA m,
In some embodiments, the mapping table is (414) stored independently from the version data structure. As a result, both are unlikely to suffer the same logical error mechanisms or loss mechanisms. For example, when the mapping table is stored independently from the version data structure, a mistake in handling the mapping table is unlikely to also be made in the version data structure.
In some embodiments, in accordance with a determination that the logical block is modified (430), the storage device (1) obtains an updated version number for the logical block, (2) maps, using the mapping table, the logical block to a new physical page of the storage device, (3) stores the updated version number for the logical block in a header of the new physical page in which the logical block is stored, and (4) stores the updated version number for the logical block in the version data structure. In some embodiments, the logical block is modified by a subsequent write request (i.e., a write request subsequent to the write request received in operation 402). In some embodiments, when the contents or a portion of the contents of a page are changed, the existing version number (e.g., from the version data structure) is read, updated (e.g., incremented), stored in the header of the new physical page, and stored back in the version data structure. For example, in some embodiments, in accordance with a determination that LBA m is modified, the storage device obtains an updated version number for LBA m (e.g., version number 2), maps LBA m to a new physical page of the storage device, stores the updated version number (e.g., version number 2) for LBA m in a header of the new physical page, and stores the updated version number (e.g., version number 2) in the version data structure for LBA m. In some embodiments, a logical block module (e.g., logical block module 226,
In some embodiments, obtaining an updated version number for the logical block comprises (432): (1) reading the version number for the logical block from the version data structure, and (2) incrementing the version number for the logical block. For example, if LBA m had version number 1 prior to LBA m being modified (e.g., by a subsequent write request), obtaining an updated version number for LBA m includes reading the version number (e.g., version number 1) for LBA m from the version data structure and incrementing the version number (e.g., from version number 1 to version number 2). In some embodiments, the version number is updated by incrementing the version number, as in the previous example where the version number is incremented by 1. In some embodiments, the version number is updated by incrementing the version number by a value other than 1 (e.g., incrementing by 5). In some embodiments, the version number is updated by modifying the version number to yield a predictable unique number. For example, in some embodiments, the version number is updated by multiplying the version number by 2 (e.g., so a version number is updated from 1 to 2 to 4 to 8, etc.).
In some embodiments, the storage device receives (434) a read request from the host (e.g., computer system 110,
In some embodiments, the storage device maps (436), using the mapping table (e.g., forward mapping table 302,
In some embodiments, the storage device performs (438) one or more operations for each logical block specified by the second set of one or more logical block addresses, including: (1) reading (440) the version number for the logical block from the version data structure, (2) reading (442) the version number for the logical block from the header of the physical page in which the logical block is stored, (3) comparing (444) the version number from the version data structure with the version number from the header of the physical page, and (4) in accordance with a determination that the version number from the version data structure is not equivalent to the version number from the header of the physical page, initiating (446) one or more recovery actions. For example, if LBA n (
In some embodiments, some (e.g., one, some, or all) of the operations performed for each logical block specified by the second set of one or more logical block addresses are performed at the storage device (e.g., storage device 120,
In some embodiments, the storage device, in accordance with a determination that, for all the logical blocks specified by the second set of one or more logical block addresses, the version number from the version data structure is equivalent to the version number from the header of the physical page, returns (448) data read from the second set of one or more logical block addresses to the host. For example, if the second set of one or more logical block addresses includes LBA n, LBA n+1, and LBA n+2, in accordance with a determination that for all the logical blocks (e.g., LBA n, LBA n+1, and LBA n+2), the version number from the respective version data structure is equivalent to the version number from the header of the respective physical page, the storage device returns data read from LBA n, LBA n+1, and LBA n+2 to the host. In some embodiments, a logical block module (e.g., logical block module 226,
A storage device (e.g., storage device 120,
In some embodiments, the storage device includes (516) one or more flash memory devices. In some embodiments, the storage device includes a storage medium (e.g., storage medium 130,
The storage device maps (504), using a mapping table (e.g., forward mapping table 302,
The storage device performs (506) one or more operations for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the first set of one or more logical block addresses, including: (1) generating (508) metadata for the subset, the metadata including a version number for the subset, (2) calculating (510) a first Cyclic Redundancy Check (CRC) checksum for the subset, and (3) storing (512) the version number for the subset and the first CRC checksum for the subset in a version data structure. In some embodiments, a subset module (e.g., subset module 256,
In some embodiments, some (e.g., one, some, or all) of the operations performed for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the first set of one or more logical block addresses are performed at the storage device (e.g., storage device 120,
As noted above, the storage device generates (508) metadata for the subset, the metadata including a version number for the subset. In some embodiments, since the subset has entries corresponding to a group of contiguous logical blocks in the logical address space of the host, the version number for the subset is maintained across a set of contiguous mapping entries, as shown in
The storage device calculates (510) a first Cyclic Redundancy Check (CRC) checksum for the subset. In some embodiments, the first CRC checksum for the subset is calculated on data that includes the mapping table entries of the subset. Using the example of subset i from
The storage device stores (512) the version number for the subset and the first CRC checksum for the subset in a version data structure. Using the example of subset i from above, the storage devices stores the version number (e.g., version number 1) for subset i in a version data structure (e.g., in version number 276 of version data structure 274-i,
Alternatively, in some embodiments, the space provided for the version number is considerably smaller (e.g., a few bits) than what would be needed to store the largest reasonably expected version number. As a result, values of the version number will not be unique for the full life of the device, but will roll-over, perhaps several times. However, in these embodiments, the number of bits provided for the version number is large enough such that there is no chance that a stale value could be mistaken for a current value.
Although the examples herein describe a separate version data structure for each subset, those skilled in the art will appreciate that the embodiments described herein may be extended to other ways to store the version number and/or CRC checksum for the subset. For example, in a simple form, the stored information may be kept as a table with as many entries as there are subsets in the mapping table, where each entry has the current (e.g., expected) version number for the subset and the CRC checksum for the subset. In some embodiments, a version module (e.g., version module 262,
In some embodiments, the mapping table is (514) stored independently from the version data structure. As a result, both are unlikely to suffer the same logical error mechanisms or loss mechanisms. For example, when the mapping table is stored independently from the version data structure, a mistake in handling the mapping table is unlikely to also be made in the version data structure.
In some embodiments, in accordance with a determination that at least one entry of the subset is modified (522): the storage device (1) obtains an updated version number for the subset, (2) calculates an updated CRC checksum for the subset, and (3) stores the updated version number for the subset and the updated CRC checksum for the subset in the version data structure. In some embodiments, the subset is modified by a subsequent write request (after the write request received by operation 502) that modifies at least one mapping table entry of the subset. In some embodiments, when the one or more mapping table entries of the subset are changed, the existing version number (e.g., from the version data structure) is read, updated (e.g., incremented), an updated CRC checksum for the subset is calculated, and the updated version number and updated CRC checksum are stored back in the version data structure. For example, in some embodiments, in accordance with a determination that LBA m is modified, the storage device obtains an updated version number for subset i (e.g., version number 2), calculates an updated CRC checksum for subset i, and stores the updated version number (e.g., version number 2) and the updated CRC checksum for subset i in the version data structure (e.g., version data structure 274-i,
In some embodiments, obtaining an updated version number for the subset comprises (524): (1) reading the version number for the subset from the version data structure, and (2) incrementing the version number for the subset. For example, if subset i had version number 1 prior to subset i being modified (e.g., by a subsequent write request to any of the logical block mapping entries of subset i), obtaining an updated version number for subset i includes reading the version number (e.g., version number 1) for subset i from the version data structure and incrementing the version number (e.g., from version number 1 to version number 2). In some embodiments, the version number is updated by incrementing the version number, as in the previous example where the version number is incremented by 1. In some embodiments, the version number is updated by incrementing the version number by a value other than 1 (e.g., incrementing by 5). In some embodiments, the version number is updated by modifying the version number to yield a predictable unique number. For example, in some embodiments, the version number is updated by multiplying the version number by 2 (e.g., so a version number is updated from 1 to 2 to 4 to 8, etc.).
In some embodiments, the storage device receives (526) a read request from the host (e.g., computer system 110,
In some embodiments, the storage device maps (528), using the mapping table (e.g., forward mapping table 302,
In some embodiments, the storage device performs (530) one or more operations for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the second set of one or more logical block addresses, including: (1) reading (532) the first CRC checksum for the subset from the version data structure, (2) calculating (534) a second CRC checksum for the subset, (3) comparing (536) the second CRC checksum for the subset with the first CRC checksum for the subset, and (4) in accordance with a determination that the second CRC checksum is not equivalent to the first CRC checksum, initiating (538) one or more recovery actions. For example, if LBA n (
In some embodiments, some (e.g., one, some, or all) of the operations performed for each subset of the mapping table that includes at least one entry corresponding to a logical block specified by the second set of one or more logical block addresses are performed at the storage device (e.g., storage device 120,
In some embodiments, the storage device, in accordance with a determination that, for all the subsets that include at least one entry corresponding to a logical block specified by the second set of one or more logical block addresses, the second CRC checksum is equivalent to the first CRC checksum, returns (540) data from the second set of one or more logical block addresses to the host. For example, if the second set of one or more logical block addresses includes LBA n, LBA n+1, and LBA n+2 (
It will be understood that, although the terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first region could be termed a second region, and, similarly, a second region could be termed a first region, without changing the meaning of the description, so long as all occurrences of the “first region” are renamed consistently and all occurrences of the “second region” are renamed consistently. The first region and the second region are both regions, but they are not the same region.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the claims. As used in the description of the embodiments and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
As used herein, the phrase “at least one of A, B and C” is to be construed to require one or more of the listed items, and this phase reads on a single instance of A alone, a single instance of B alone, or a single instance of C alone, while also encompassing combinations of the listed items such “one or more of A and one or more of B without any of C,” and the like.
As used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in accordance with a determination” or “in response to detecting,” that a stated condition precedent is true, depending on the context. Similarly, the phrase “if it is determined [that a stated condition precedent is true]” or “if [a stated condition precedent is true]” or “when [a stated condition precedent is true]” may be construed to mean “upon determining” or “in response to determining” or “in accordance with a determination” or “upon detecting” or “in response to detecting” that the stated condition precedent is true, depending on the context.
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain principles of operation and practical applications, to thereby enable others skilled in the art.
This application claims priority to U.S. Provisional Application No. 62/082,851, filed Nov. 21, 2014, which is hereby incorporated by reference in its entirety.
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