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`
`(54) NON-VOLATILE MEMORY DATA STORAGE
`SYSTEM WITH RELIABILITY
`MANAGEMENT
`
`(75)
`
`Inventors:
`
`ROGER CHIN, San Jose, CA
`(US); Gary Wu, Fremont, CA (US)
`
`Correspondence Address:
`Tung & Associates
`Suite 120
`838 W. Long Lake Road
`Bloomfield Hills, MI 48302 (US)
`
`(73)
`
`Assignee:
`
`Nanostar Corporation, U.S.A
`
`(21)
`
`Appl. No.:
`
`12/471,430
`
`(22)
`
`Filed:
`
`May 25, 2009
`
`Related U.S. Application Data
`
`(63)
`
`Continuation-in-part of application No. 12/218,949,
`filed on Jul. 19, 2008, Continuation-in-part of applica-
`tion No. 12/271,885, filed on Nov. 15, 2008, Continu-
`ation-in-part of application No. 12/372,028, filed on
`Feb. 17, 2009.
`
`(10)
`(43) viiu.oei...
`
`dan
`
`31 5 iu10
`
`Publication Classification
`
`'
`
`Int. Cl.
`G06F 12/16
`G06F 12/02
`G06F 13/28
`G06F 11/14
`G06F12/08
`
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`
`............... 714/6; 711/103; 710/22; 711/114;
`U.S. Cl.
`711/206; 711/118; 711/E12.008; 711/E12.103;
`711/E12.017;714/E11.127
`
`ABSTRACT
`
`(51)
`
`(52)
`
`(57)
`
`A non-volatile memory data storage system, comprising: a
`host interface for communicating with an external host; a
`main storage including a first plurality of flash memory
`devices, wherein each memory device includes a second plu-
`rality of memory blocks, and a third plurality of first stage
`controllers coupled to the first plurality of flash memory
`devices; and a second stage controller coupled to the host
`interface and the third plurality of first stage controller
`through an internal interface, the second stage controller
`being configured to perform RAID operation for data recov-
`ery according to at least one parity.
`
`100
`Reliability Measurement By
`e.g., MTBF, UBER
`
`Host
`
`Host Interface
`120
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`
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`Micron v. Vervain
`IPR2021-01550
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`Micron v. Vervain
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`Micron v. Vervain
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`Micron v. Vervain
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`Micron v. Vervain
`IPR2021-01550
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`Micron Ex. 1030, p. 13
`Micron v. Vervain
`IPR2021-01550
`
`

`

`Patent Application Publication
`
`Jan. 21, 2010 Sheet 13 of 16
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`Micron Ex. 1030, p. 14
`Micron v. Vervain
`IPR2021-01550
`
`

`

`Patent Application Publication
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`Micron Ex. 1030, p. 15
`Micron v. Vervain
`IPR2021-01550
`
`

`

`Patent Application Publication
`
`Jan. 21, 2010 Sheet 15 of 16
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`Micron Ex. 1030, p. 16
`Micron v. Vervain
`IPR2021-01550
`
`

`

`Patent Application Publication
`
`Jan. 21, 2010 Sheet 16 of 16
`
`US 2010/0017650 Al
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`Micron Ex. 1030, p. 17
`Micron v. Vervain
`IPR2021-01550
`
`

`

`US 2010/0017650 Al
`
`Jan. 21, 2010
`
`NON-VOLATILE MEMORY DATA STORAGE
`SYSTEM WITH RELIABILITY
`MANAGEMENT
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`The present invention is a continuation-in-part
`[0001]
`application of U.S. Ser. No. 12/218,949, filed on Jul. 19,
`2008, ofU.S. Ser. No. 12/271,885, filed onNov. 15,2008, and
`of U.S. Ser. No. 12/372,028, filed on Feb. 17, 2009.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`[0002]
`The present invention relates to a non-volatile
`[0003]
`memory (NVM) data storage system with reliability manage-
`ment, in particular to an NVM data storage system which
`includes a main storage of, e.g., solid state drive (SSD), or
`memory card modules, in which the reliability of the stored
`data is improved by utilizing distributed embedded reliability
`management in a two-stage control architecture. The system
`is preferably configured as RAID-4, RAID-5 or RAID-6 with
`one or more remappable spare modules, or with one or more
`spare blocks in each module, to further prolong the lifetime of
`the system.
`[0004]
`2. Description of Related Art
`[0005]
`Memory modules made of non-volatile memory
`devices, in particular solid state drives (SSD) and memory
`cards which include NAND Flash memory devices, have
`great potential to replace hard disk drives (HDD) because
`they have faster speed, lower power consumption, better rug-
`gedness and no moving parts in comparison with HDD. A
`data storage system with such flash memory modules will
`become more acceptable if its reliability quality can be
`improved, especially if the endurance cycle issue of MLCxr,
`(N=2, 3 or 4, i.e. multi-level cell with 2 bits per cell, 3 bits per
`cell and 4 bits per cell) is properly addressed.
`[0006]
`One of the major failure symptoms affecting the
`silicon wafer yield of NAND flash devices is the reliability
`issue. By providing a data storage system with better capa-
`bility of handling reliability issues, it does not only improve
`the quality of the data storage system but can also increase the
`wafer yield of flash devices. The utilization rate out of each
`flash device wafer can be greatly increased, since the system
`can use flash devices that are tested out with inferior criteria.
`[0007]
`As the process technology for manufacturing
`NAND flash devices keeps advancing and the die size keeps
`shrinking,
`the value of Mean-Time-Between/To-Failure
`(MTBF/MTTF) of the NAND-flash-based SSD system
`decreases and the value of Uncorrectable-Bit-Error-Rate
`(UBER) increases. The typical SSD UBER is usually one
`error for 1015 bits read.
`[0008]
`Another aspect that affects reliability characteristics
`of the flash-based data storage system is write amplification.
`The write amplification factor (WAF) is defined as the data
`size written into a flash memory versus the data size from
`host. For a typical SSD, the write amplification factor can be
`30 (i.e., 1 GB of data that are written to the flash causes 30 GB
`of program/erase cycles).
`[0009] A data storage system with good reliability manage-
`ment is capable of improving MTBF and UBER and reducing
`WAF, while enjoys the cost reduction resulting from shrunk
`
`die size. Thus, a data storage system with good reliability
`management is very much desired.
`
`SUMMARY OF THE INVENTION
`
`In view of the foregoing, an objective of the present
`[0010]
`invention is to provide an NVM data storage system with
`distributed embedded reliability management in a two stage
`control architecture, which is in contrast to the conventional
`centralized single controller structure, so that reliability man-
`agement loading can be shared among the memory modules.
`The reliability quality of the system is thus improved.
`[0011]
`Two important measures of reliability for flash-
`based data storage system are MTBF and UBER. ECC/EDC,
`BBM, WL and RAID schemes are able to improve the reli-
`ability of the system, and thus improve the MTBF and UBER.
`The present invention proposes several schemes to improve
`WAF and other reliability factors; such schemes include but
`are not limited to (a) distributed channels, (b) spare block in
`the same or a spare module for recovering data in a defected
`block, (c) cache scheme, (d) double-buffer, (e) reconfigurable
`RAID structure, and (f) region arrangement by different types
`of memory devices. In the distributed channels architecture,
`preferably, each channel includes a double-buffer, a DMA, a
`FIFO, a first stage controller and a plurality of flash devices.
`This distributed channel architecture will minimize the
`unnecessary writes into flash devices due to the indepen-
`dently controlled write for each channel.
`[0012]
`To improve reliability of the data storage system, the
`system is configured preferably by RAID 4, RAID-5 or
`RAID-6 and has recovery and block repair functions with
`spare block/module. The once defected block is replaced by
`the spare block, either in the same memory module or in a
`spare module, with the same logical block address but
`remapped physical address.
`[0013]
`More specifically, the present invention proposes an
`NVM data storage system comprising: a host interface for
`communicating with an external host; a main storage includ-
`ing a first plurality of flash memory devices, wherein each
`memory device includes a second plurality of memory
`blocks, and a third plurality of first stage controllers coupled
`to the first plurality of flash memory devices; and a second
`stage controller coupled to the host interface and the third
`plurality of first stage controller through an internal interface,
`the second stage controller being configured to perform
`RAID operation for data recovery according to at least one
`parity.
`Preferably, in the NVM data storage system, the first
`[0014]
`plurality of flash devices are allocated into a number of dis-
`tributed channels, wherein each channel includes one of the
`first stage controllers and further includes a DMA and a
`buffer, coupled with the one first stage controller in the same
`channel.
`Preferably, in the NVM data storage system, the
`[0015]
`controller maintains a remapping table for remapping a
`memory block to another memory block.
`[0016]
`Preferably, the NVM data storage system further
`comprises an additional, preferably detachable, memory
`module which can be used as swap space, cache or confined,
`dedicated hot zone for frequently accessed data.
`[0017]
`Preferably, each channel of the NVM data storage
`system comprises
`a
`double-buffer. The double-buffer
`includes two SRAM buffers which can operate simulta-
`neously.
`
`Micron Ex. 1030, p. 18
`Micron v. Vervain
`IPR2021-01550
`
`

`

`US 2010/0017650 Al
`
`Jan. 21, 2010
`
`2
`
`Also preferably, the NVM data storage system
`[0018]
`implements a second stage wear leveling function. The sec-
`ond wear leveling is performed across the memory modules
`("globally"). The main storage is divided into a plurality of
`regions, and the controller performs the second stage wear
`leveling operation depending on an erase count associated
`with each region. The system maintains a second wear level-
`ing table which includes the address translations between the
`logical block addresses within each region and the logical
`block addresses of the first stage memories.
`[0019]
`In another aspect, the present invention discloses an
`NVM data storage system which comprises: a main storage
`including a plurality of memory modules, wherein the data
`storage system performs a reliability management operation
`on each of the plurality of memory modules individually; and
`a controller coupled to the main storage and configured to
`perform at least two kinds of RAID operations for storing data
`according to a first and a second RAID structure, wherein data
`is first stored in the main storage according to the first RAID
`structure, e.g., RAID-0 or RAID-1 and is reconfigurable to
`the second RAID structure such as RAID-4, 5 or 6.
`[0020]
`In another aspect, the present invention discloses an
`NVM data storage system which comprises: a host interface
`for communicating with an external host; a main storage
`including a plurality of memory modules, wherein the data
`storage system performs a distributed reliability management
`operation on each of the plurality of memory modules indi-
`vidually, the reliability management operation including at
`least one of error correction coding, error detection coding,
`bad block management, wear leveling, and garbage collec-
`tion; and a controller coupled to host interface and to the main
`storage, the controller being configured to perform RAID-4
`operation for data recovery
`[0021]
`In another aspect, the present invention discloses an
`NVM data storage system which comprises: data storage
`system comprising: a main storage including a plurality of
`flash devices divided into a plurality of channels; a controller
`configured to reduce erase/program cycles of the main stor-
`age; a memory module coupled to the controller and serving
`as cache memory; wherein reliability management operations
`including error correction coding, error detection coding, bad
`block management and wear leveling are performed on each
`channel individually.
`[0022]
`It is to be understood that both the foregoing general
`description and the following detailed description are pro-
`vided as examples, for illustration rather than limiting the
`scope of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other objects and features of the
`[0023]
`present invention will become better understood from the
`following descriptions, appended claims when read in con-
`nection with the accompanying drawings.
`[0024]
`FIG. 1A illustrates a non-volatile memory data stor-
`age system with reliability management in a two stage control
`architecture according to the present invention. The system
`includes a host interface, a controller, and a main storage
`including multiple memory modules.
`[0025]
`FIG. 1B shows an embodiment with distributed
`channels and distributed embedded reliability management.
`[0026]
`FIG. 2 is a block diagram of the main storage 160
`including regions with different capacity indexes.
`[0027]
`FIG. 3 shows an embodiment of the present inven-
`tion employing RAID-4 configuration.
`
`FIG. 4 shows an embodiment of the present inven-
`[0028]
`tion employing RAID-5 configuration, with a spare module.
`[0029]
`FIG. 5 shows an embodiment with block-level
`repair and recovery functions.
`[0030]
`FIG. 6 shows an embodiment with block-level
`repair and recovery functions, wherein a memory module
`reserves one or more spare blocks to repair a defected block in
`the same memory module. A remapping table shows the
`remapping information for the defected blocks.
`[0031]
`FIG. 7 shows an embodiment of the present inven-
`tion employing RAID-6 configuration, wherein a memory
`module reserves one or more spare blocks to repair a defected
`block in the same memory module.
`[0032]
`FIG. 8 shows an embodiment of the present inven-
`tion which includes a memory module which is used as a
`swap space or cache. The memory module can be detachable.
`[0033]
`FIG. 9 illustrates that the cache 180 stores the ran-
`dom write data to reduce the Write Amplification Factor
`(WAF). The dual-buffer store the sequential write data and
`also store the data flush from the cache 180 before storing
`these data to the main storage 160.
`[0034]
`FIG. 10 shows the data paths of read hit, read miss,
`write hit, and write miss,
`[0035]
`FIG. 11 shows the first stage wear leveling tables.
`[0036]
`FIG. 12 shows the address translation for segment
`address, logical block address ID, logical block address and
`physical block address; it also shows the erase/program count
`table for wear leveling.
`[0037]
`FIG. 13 is a flowchart showing second stage wear
`leveling operation based on the segment erase count.
`[0038]
`FIG. 14 shows a block diagram of an embodiment of
`the system according to the present invention, which includes
`BIST/BISD/BISR
`(Built-In-Self-Test/Diagnosis/Repair)
`functions.
`[0039]
`FIG. 15 shows an embodiment of the present inven-
`tion wherein down-grade or less endurable flash devices are
`used.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The present invention will now be described in
`[0040]
`detail with reference to preferred embodiments thereof as
`illustrated in the accompanying drawings.
`[0041]
`FIG. 1A shows a NVM storage system 100 accord-
`ing to the present invention, which employs distributed
`embedded reliability management in a two stage control
`architecture (the terms "distributed" and "embedded" will be
`explained later). The reliability management architecture
`according to the present invention provides great benefit
`because good reliability management will not only improve
`the quality of the data and prolong the lifetime of the storage
`system, but also increase the manufacturing yield of flash
`memory device chips in a semiconductor wafer, since the
`number of usable dies increases.
`[0042]
`The system 100 includes a host interface 120, a
`controller 142 and a main storage 160. The host interface 120
`is for communication between the system and a host. It can be
`SATA, SD, SDXC, USB, UFS, SAS, Fiber Channel, PCI,
`eMMC, MMC, IDE or CF interface. The controller 142 per-
`forms data read/write and reliability management operations.
`The controller 142 can be coupled to the main storage 160
`through any interface such as NAND, LBA_NAND,
`BA_NAND, Flash_DIMM, ONFI NAND, Toggle-mode
`NAND, SATA, SD, SDXC, USB, UFS, PCI or MMC, etc.
`
`Micron Ex. 1030, p. 19
`Micron v. Vervain
`IPR2021-01550
`
`

`

`US 2010/0017650 Al
`
`Jan. 21, 2010
`
`The main storage 160 includes multiple memory modules
`161-16N, each including multiple memory devices 61-6N. In
`one embodiment, the memory devices are flash devices,
`which maybe SLC (Single-Level Cell), MLC (Multi-Level
`Cell, usually meaning 2 bits per cell), MLC3(3 bits per cell),
`MLC,, (4 bits per cell) or MLCxs (5 bits per cell) memory
`devices. Preferably, the system 100 employs a two-stage reli-
`ability control scheme wherein each of the memory modules
`161-16N is provided with a first stage controllers 1441-144N
`for embedded first stage reliability management, and the con-
`troller 142 performs a global second stage reliability manage-
`ment.
`Referring to FIG. 1B, the reliability management
`[0043]
`tasks include one or more of error correction coding/error
`detection coding (ECC/EDC), bad block management
`(BBM), wear leveling (WL) and garbage collection (GC).
`The ECC/EDC and BBM operations are well known by one
`skilled in this art, and thus they are not explained here. The
`garbage collection operation is to erase the invalid pages and
`set the erased blocks free. If there is one or more valid pages
`residing in a to-be-erase block, such pages are reallocated to
`another block which has an available space and is not to be
`erased. The wear leveling operation reallocates data which
`are frequently accessed to a block which is less frequently
`accessed. It improves reliability characteristics including
`endurance, read disturbance and data retention. The realloca-
`tion of data in a block causes the flash memory cells to be
`re-charged or re-discharged. The threshold voltages of those
`re-written cells are restored to the original target levels; there-
`fore the data retention and read disturbance characteristics are
`improved. Especially, because the retention quality of the
`MLCx3, MLC,4 flash devices is worse and read disturbance
`thereof is severer than MLCxz flash devices, WL is even more
`important when MLCx3, MLC,4 flash devices are employed
`in the main storage 160. According to the present invention,
`such reliability management operations are performed in an
`embedded fashion, that is, they are performed on each storage
`module individually, at least as a first stage reliability man-
`agement. The controller 142 may perform a second stage
`reliability management across all or some of the storage mod-
`ules.
`The system 100 is defined as having "distributed"
`[0044]
`embedded reliability management architecture because it
`includes distributed channels, each of which is subject to
`embedded reliability management. In FIG. 1B, as an
`example, the main storage 160 includes four distributed chan-
`nels (only two channels are marked for simplicity of the
`drawing), and each channel is provided with a memory mod-
`ule, i.e., the memory modules 161-164. The channels are
`referred as ports also. Each channel is also provided with an
`interface 401-404, preferably including a DMA (Direct-
`Memory-Access, or ADMA, i.e. Advanced-DMA) and a
`FIFO (not shown), in correspondence with each memory
`module 161-164. The ADMA can adopt a scatter-and-gather
`algorithm to increase transfer performance.
`[0045]
`The controller 142 is capable of performing RAID
`operation, such as RAID-4 as shown in FIG. 1B, or other
`types of RAID operations such as RAID-0, 1, 2, 3, 5, 6, etc.
`(For details of RAID, please refer to the parent application
`U.S. Ser. No. 12/218,949.) In RAID-4 structure, the system
`generates a parity for each row of data stored (A-, B-, C-, and
`D-parity), and the parity bits are stored in the same module.
`Preferably, the controller 142 includes a dedicated hardware
`XOR engine 149 for generating such parity bits.
`
`The system 100 has recovery and block repair func-
`[0046]
`tions, and is capable of performing remapping operations to
`remap data access to a new address. There are several ways to
`allow for data remapping, which will be further described
`later with reference to FIGS. 4-7. In FIG. 1B, which is one
`among several possible schemes in the present invention,
`each module 161-164 reserves at least one spare block
`(spare-1 to spare-4) which is not used as a working space. As
`long as a block in the working space is defected, the defected
`block will be remapped by using the spare block in the same
`module (spare-1 in module 161, spare-2 in module 162, etc.).
`The module with the defected block will be repaired and
`function as normal after the remapping; thus the data storage
`system can continue its operations after the repair. The parity
`blocks (A-, B-, C-, and D-parity) can be used for data recov-
`ery and rebuild. More details of this scheme will be described
`later in FIG. 7.
`[0047]
`The main storage 160 can be divided into multiple
`regions in a way as shown in FIG. 2. Each region includes one
`segment in each memory module 161-16N. Each segment
`may include multiple blocks. In this embodiment, as shown in
`FIG. 2, a memory module may include memories of different
`types, i.e., two or more of SLC, MLC, MLCx3 , MLCx4
`memories. It can also include down-grade memories which
`have less than 95% usable density. The memories with the
`best endurance can be grouped into one region and used for
`storing more frequently accessed data. For example, in this
`embodiment, the Region-1 includes SLC flash memories and
`can be used as a cache memory.
`[0048]
`According to the present invention, a capacity index
`is defined for each region. Different region can have different
`capacity index depending on the type of flash memory
`employed by that region. The index is related to endurance
`quality of the flash devices. The endurance specification of
`SLC usually achieves 100 k. The endurance specification of
`MLCxz is 10 k, but it is 2 k for MLC3 and 500 for MLC,4.
`Thus, for example, we can define the capacity index as 1 for
`MLC,4, 4 for MLCx3, 20 for MLCxz and 200 for SLC flash, in
`correspondence to their respective endurance characteristics.
`The capacity index is useful in wear leveling operation, espe-
`cially when heterogeneous regions are employed, with dif-
`ferent flash devices in different regions.
`[0049]
`The main storage 160 is configured under RAID
`architecture. In one embodiment, it can be configured by
`RAID-4 architecture as shown in FIG. 3. In this example the
`main storage 160 includes four modules M1-M4. Each mod-
`ule includes multiple memory devices and each memory
`device includes multiple memory blocks (only three blocks
`per device is shown, but the actual block number is much
`more). The data are written across the modules M1-M3 by
`row, and each row is given a parity (p) which is stored in the
`module M4. Any data lost in a block (i.e., a defected block)
`can be recovered by the parity bits.
`[0050]
`FIG. 4 shows another embodiment. In this embodi-
`ment, The main storage 160 is configured by RAID-5 archi-
`tecture wherein the parity bits (p) are scattered to all the
`memory modules. In this example the main storage 160
`includes four modules M1-M4 and it further includes a hot
`spare module. Each module includes multiple memory
`devices and each memory device includes multiple memory
`blocks (only three blocks per device is shown, but the actual
`block number is much more). The data are written across the
`modules M1-M4 by row, and each row is given a parity (p). In
`case a defected block is found in a module, such as M2 as
`
`Micron Ex. 1030, p. 20
`Micron v. Vervain
`IPR2021-01550
`
`

`

`US 2010/0017650 Al
`
`Jan. 21, 2010
`
`4
`
`shown in the left hand side of the figure, the lost data can be
`recovered with the help by the parity. And as the right hand
`side of the figure shows, the once defected module becomes a
`spare module after the defected module is remapped. A user
`may later replace the once defected module by a new module.
`[0051]
`FIG. 5 shows another embodiment of the present
`invention, which allows block-level repair. In case one or
`more defected (failure) blocks are found, the spare blocks in
`the spare module can be used to rebuild/repair the failing
`blocks, including the parity blocks. The parity (p) can help to
`recover the lost data in the defected block. If the defected
`block is the parity block, the parity can be re-generated and
`rewritten to the spare device. The first column in the remap-
`ping table records the mapping information of the first failure
`block for that row. The second column records the mapping
`information of the second failure block for that same row. In
`the shown example, C1 is the first failure block in the row
`consisting of C1, p, C2, and C3, and E3 is the first failure
`block in the row consisting of El, E2, E3, and p. Thus, the
`remapping table records the information such that any access
`to the original C1 and E3 blocks are remapped to the replacing
`blocks in the spare module. The scheme allows for a second
`failure block in the same row (such as C3), and the remapping
`table records it in the second column.
`[0052]
`In the embodiments shown in FIGS. 4 and 5, the
`total number of spare blocks in the spare module is the same
`as the number of blocks in each module. However, a spare
`module with smaller number of spare blocks can be employed
`for saving costs. Th