KR20210089055A - Flash memory storage with improved erase performance and method thereof - Google Patents

Abstract

According to an embodiment of the present invention, a method of improving erase performance of a flash memory storage device includes the steps of: receiving a data collection command including preservation data information about the data to be stored in the preservation block, which is a block in which data which needs continuous preservation from the host is stored; and moving data corresponding to the preservation data information to the preservation block in response to the data collection command.

Description

FLASH MEMORY STORAGE WITH IMPROVED ERASE PERFORMANCE AND METHOD THEREOF

The present invention relates to a flash memory storage device with improved erasing performance and a method therefor.

Flash memory is a non-volatile memory storage medium and is being used as a next-generation storage device in various forms such as a solid state drive (SSD) or USB memory based on various advantages such as fast read speed, stability, and low power consumption. However, flash memory has limitations due to its physical characteristics.

First, overwrite is not possible. Since new data cannot be overwritten on a page in which data has already been written, when data at an already written logical address needs to be updated with new data, new data is written to a separate physical area and then the existing data is invalidated. Second, it provides an erase function. Erasing is a function that changes invalidated pages to a usable state by being updated with new data.

In addition, the process of selecting a block to be erased and performing erase in order to secure a page to write data in the flash memory is called garbage collection (GC). GC is a larger unit than write/read, so valid pages may remain in the block. Valid pages are protected by copying them back to a separate area. Copyback safely manages data, but it has a negative impact on performance because it has to perform a write operation other than the write requested by the host. A write amplification factor (WAF) is used as an index indicating the degree of copyback, and it is important to reduce the WAF in consideration of the performance of the flash memory storage device. The next limitation is that NAND flash memory chips have a limited lifespan. A NAND flash memory chip can perform “write-erase” only a limited number of times with a limited lifespan. Therefore, if the WAF mentioned in the second constraint is high, the lifespan of the flash memory is hindered.

Accordingly, there is a need for a flash memory storage device with improved erasing performance with reduced WAF and a method therefor by reducing the number of copybacks.

Korean Patent Publication No. 10-2015-0106777 (published on September 22, 2015)

An object of the present invention is to provide a flash memory storage device and method for overcoming the problems of the prior art, which reduce WAF and ultimately improve write performance and lifespan of the flash storage device.

In order to achieve the above object, a method for improving erase performance of a flash memory storage device according to an embodiment of the present invention includes preservation data information, which is information about data to be stored in a preservation block, which is a block in which preservation target data is stored, from a host. receiving a gather command; and moving data corresponding to the stored data information to the storage block in response to the gather command.

Preferably, the moving to the preservation block comprises: converting a logical address of a page corresponding to each data corresponding to the preserved data information into a physical address based on a flash translation layer (FTL); using the converted physical address to invalidate a page corresponding to each data corresponding to the stored data information; and writing data stored in the invalidated page to the retention block.

Preferably, the moving to the preservation block comprises: converting a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL; setting a Gather Mark on a page corresponding to each data corresponding to the stored data information by using the converted physical address; and writing data stored in the page in which the gather mark is set to the retention block when garbage collection (GC) is performed on the block including the page in which the gather mark is set.

Preferably, the preservation data information may include a start logical address of data to be stored in the preservation block and the number of target pages.

Preferably, the moving to the retention block may include storing data corresponding to the number of target pages from the start logical address to be physically continuous in the retention block.

In addition, the flash memory storage device with improved erasing performance according to an embodiment of the present invention for achieving the above object includes preservation data information, which is information about data to be stored in a preservation block, which is a block in which preservation target data is stored, from a host. a receiving unit for receiving a gather command; and a control unit for moving data corresponding to the stored data information to the storage block in response to the gather command.

Preferably, the control unit converts a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL, and uses the converted physical address to correspond to the stored data information A page corresponding to each data to be used may be invalidated, and data stored in the invalidated page may be written to the retention block.

Preferably, the control unit converts a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL, and uses the converted physical address to correspond to the stored data information When a gather mark is set on a page corresponding to each data to be collected, and garbage collection is performed on a block including the page on which the gather mark is set, data stored in the page on which the gather mark is set can be written to the retention block.

Preferably, the preservation data information may include a start logical address of data to be stored in the preservation block and the number of target pages.

Preferably, when the control unit moves the data corresponding to the preservation data information to the preservation block, the data corresponding to the target number of pages from the start logical address may be physically stored in the preservation block.

According to an embodiment of the present invention, since data of a specific logical address already written in the flash memory storage device can be physically collected, WAF can be reduced, write performance is improved, and the lifespan of the flash storage device can be improved. .

1 is a flowchart illustrating a method for improving erase performance of a flash memory storage device according to an embodiment of the present invention.
2 is a flowchart illustrating a method of moving data to a retention block by a flash memory storage device according to an embodiment of the present invention.
3 is a flowchart illustrating a method of moving data to a retention block by a flash memory storage device according to another embodiment of the present invention.
4 is a block diagram of a flash memory storage device with improved erase performance according to an embodiment of the present invention.
5 is a diagram for explaining a gather command according to an embodiment of the present invention.
6 is a view for explaining an EAGER GATHER according to an embodiment of the present invention.
7 is a view for explaining an ASYNC GATHER according to an embodiment of the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments will be described in detail with reference to the drawings. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. and/or includes a combination of a plurality of related description items or any of a plurality of related description items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it should be understood that other components may exist in between. something to do. On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Throughout the specification and claims, when a part includes a certain element, it means that other elements may be further included, rather than excluding other elements, unless specifically stated to the contrary.

The flash memory storage device of the present invention may refer to a flash memory-based storage device such as a solid state drive (SSD), an embedded multi-media card (eMMC), and a USB memory.

Most conventional flash memory storage devices use page mapping FTL for high performance, and when selecting a block to be erased in the GC process, a greedy algorithm that selects a block with the most invalid pages is used. do. However, when using this method, the following problems arise.

In practical applications, data pages often have different lifetimes. Here, the lifetime refers to the interval between writing and invalidating a specific page, and invalidation is done through deletion or update of data. When these pages are located in one physical area without distinction, a block containing a page that will not be invalidated for a long time by the greedy algorithm becomes the target of GC, and the page is repeatedly copied back to achieve a high WAF. cause. However, since high WAF causes performance degradation and lifetime degradation of flash memory devices, there has been a movement to recognize this problem and to manually or automatically arrange data differently according to its characteristics.

1 is a flowchart illustrating a method for improving erase performance of a flash memory storage device according to an embodiment of the present invention.

In step S110, the flash memory storage device receives, from the host, a gather command including preservation data information, which is information about data to be stored in a retention block, which is a block in which storage target data is stored.

That is, the host may transmit a gather command to the flash memory storage device in order to move and store data that is already stored in the flash memory storage device and which is highly likely to be continuously stored without being changed to the retention block.

In other words, the flash memory storage device may provide a means for moving data already stored in the flash memory to the retention block by providing an interface for the gather command to the host.

This may be to reduce the number of times that a copyback occurs by performing garbage collection on a block in which the data is stored by allowing the flash memory storage device to store data to be continuously stored without being changed in a specific retention block.

Meanwhile, the preservation data information may include a logical address of data to be stored in the preservation block. That is, the host selects data to be stored in the retention block according to a predetermined criterion, and transmits the logical address of the data to the flash memory storage device so that the gather command is executed.

Finally, in step S120, the flash memory storage device moves the data corresponding to the save data information to the save block in response to the gather command.

That is, when the flash memory storage device receives the gather command, the data corresponding to the stored data information can be moved from the previously stored block to the reserved block.

Meanwhile, a detailed method for the flash memory storage device to move data corresponding to the preservation data information to the preservation block will be described in detail with reference to FIGS. 2 and 3 .

In another embodiment, the preservation data information may include a start logical address of data to be stored in the preservation block and the number of target pages.

In this case, the flash memory storage device may move data corresponding to the number of target pages from the start logical address to the retention block.

For example, the flash memory storage device may receive the start logical address and target number of pages of data to be stored in the retention block as parameters of the gather command.

In another embodiment, the flash memory storage device may store data corresponding to the target number of pages from the start logical address to be physically contiguous in the retention block.

That is, when the flash memory storage device moves data corresponding to the number of target pages from the start logical address to the retention block, the data may be moved and rearranged by moving the data to a physical address contiguous to the retention block.

For example, when the starting logical address is A and the target number of pages is B, the flash memory storage device stores data (pages) of physical addresses corresponding to A to A+B from C to C+, which are consecutive physical addresses of the retention block. You can store up to B.

For example, referring to FIG. 5 , the flash memory storage device may receive a command from the host through the gather(Start_LBA, Length) interface, and move the data of the normal block located in the normal region to the retention block located in the gathered region. .

As described above, if the present invention is used, data pages that greatly contribute to copyback are isolated in a separate area (eg, a retention block), or data stored in a logically continuous address area is stored in one physical area (eg, a retention block). ) can be physically rearranged. That is, by giving the user (host) the right to designate the physical location of data, it is possible to present a solution in the WAF dimension that adversely affects the performance and lifespan of the flash memory storage device. As an example, by separating a frozen page that is no longer updated and thus invalidated into a separate area by utilizing the present invention, a phenomenon in which WAF increases due to continuous copyback of valid pages can be avoided. In particular, the present invention is highly likely to be utilized by administrator-level users who understand the characteristics of data in an environment such as a data server that manages large amounts of data. In addition, the present invention can be used as a data relocation tool to improve the performance of a flash memory storage device, such as disk defragmentation provided by Windows, by combining automated clustering technology in consideration of data characteristics in the future.

2 is a flowchart illustrating a method (eager gather) for moving data to a retention block in a flash memory storage device according to an embodiment of the present invention.

In step S210, the flash memory storage device converts a logical address of a page corresponding to each data corresponding to the preserved data information into a physical address based on a flash translation layer (FTL).

Here, the flash memory storage device includes an FTL inside, and the FTL performs address mapping that converts a logical address of the host's file system into a physical address of the flash memory. can That is, the FTL has a table that maps logical addresses and physical addresses, so that address mapping can be performed.

In step S220, the flash memory storage device invalidates a page corresponding to each data corresponding to the stored data information by using the converted physical address.

That is, the flash memory storage device may invalidate a page corresponding to the converted physical address in the flash memory.

Finally, in step S230, the flash memory storage device writes the data stored in the invalidated page to the retention block.

Also, the flash memory storage device may store data stored in the invalidated page in the retention block. Furthermore, the flash memory storage device may update the physical address of the address mapping table included in the FTL to a new address corresponding to the retention block.

As a result, in the flash memory storage device, a newly written physical address may exist in a separate area (ie, an address corresponding to a retention block) from a physical address continuously written through an existing write or GC. In the original page mapping FTL, new data is written in the append method. That is, when writing new data, updating existing data, or writing to flash memory due to GC occurs, writing can be performed in a continuous physical area regardless of the type. On the other hand, when a new write is performed through this interface, the write is performed in a separate area separate from the continuous physical area where the existing write stream is performed.

For example, referring to FIG. 6 , the flash memory storage device may invalidate page 6 of BLOCK 1 and page 7 of BLOCK 2, and then move it to the retention block BLOCK N and store it.

3 is a flowchart illustrating a method (async gather) for moving data to a retention block in a flash memory storage device according to another embodiment of the present invention.

In step S310, the flash memory storage device converts a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL.

In step S320, the flash memory storage device sets a gather mark on a page corresponding to each data corresponding to the stored data information by using the converted physical address.

That is, asynchronous gather sets only the gather mark without waiting for the data of the logical address to which the gather command has been received to be stored in the retention area, unlike the eager gather described above.

In other words, the flash memory storage device does not directly write the data of the logical address to which the gather command has been received to the storage area, but sets only the gather mark. Then, the flash memory storage device may complete the data movement by separately performing a write operation thereafter.

Finally, in step S330, when the flash memory storage device performs garbage collection on a block including a page in which the gather mark is set, data stored in the page in which the gather mark is set is written to the retention block.

That is, the flash memory storage device may wait until garbage collection is performed on the block including the page in which the gather mark is set. And, when garbage collection is performed on the block, the flash memory storage device may move the page on which the gather mark is set to the retention block.

In other words, when the asynchronous gather performs copyback according to garbage collection in this way, if data corresponding to the page on which the gather mark is set becomes the target of copyback, the data may be separated into preservation blocks. Accordingly, the asynchronous gather shows better performance than the eager gather method because it completes immediately after displaying the gather mark when a gather instruction is issued.

For example, referring to FIG. 7 , the flash memory storage device sets a GATHER MARK on page 6 of BLOCK 1 and page 7 of BLOCK 2, and then sets the retention block ( It can be saved by moving it to BLOCK N).

At this time, in order to use asynchronous gather, additional memory for GC Mark is required, and the time when the data of the logical address that is the target of the gather command is separated is the time when the data of the logical address that is the target of the gather command becomes the target of GC, not the time when the gather command is received Therefore, the data of the logical address that the host has issued a single gather command to may be copied at different times.

Therefore, when used for frozen page separation mentioned in the invention as an example, the objects to be separated are data that will no longer be invalidated, so it only needs to be isolated in a separate physical space regardless of the data order, so asynchronous gather can have strengths. On the other hand, if you want to gather data into consecutive physical addresses because the data lifespan of consecutive logical addresses is similar, it may be better to use eager gather.

Meanwhile, the performance evaluation results for the present invention are as follows. In this performance evaluation, a scenario in which a frozen page, which is no longer updated, is divided into a separate physical area is assumed as an application method of the present invention. In fact, in a typical OLTP workload, log data that records the history of transaction processing exists, and the performance was evaluated by modeling the case through FIO, an input/output generation tool.

At this time, the benchmark execution process is as follows.

1. Fill 80% of the SSD area with random writes. At this time, the total amount of random writes requested by the host is three times the size of the entire database.

2. When the present invention is applied, a gather command is issued for the logical data of the written 80% area.

3. Random write to the remaining 20% area of SSD.

The final WAF for this is shown in Table 1 below.

Config Host Requested Pages Copy-backed Pages WAF Original 2,371,531 6,377,064 3.69 GATHER 2,362,923 666,528 1.28

Through the separation of the frozen page to which the present invention is applied, the WAF is reduced from 3.69 to 1.28, and the WAF improvement effect of 65% can be confirmed. This shows the applicability of the present invention as an effect obtained by separating data having different characteristics in separate physical spaces. Even in the initial 80% of the above experiment, it was confirmed that the WAF decreased to 1.14 when sequential writing rather than random writing was performed in order to obtain an optimal result. This reduction in WAF is more meaningful in that the performance improvement can be seen as the amount of write processing inside the SSD is reduced. FIG. 4 is a flash memory storage with improved erase performance according to an embodiment of the present invention. It is a block diagram of the device.

Referring to FIG. 4 , a flash memory storage device 400 with improved erase performance according to an embodiment of the present invention includes a receiver 410 and a controller 420 .

The receiving unit 410 receives, from the host, a gather command including preservation data information, which is information about data to be stored in a preservation block, which is a block in which data to be preserved is stored.

The control unit 420 moves the data corresponding to the stored data information to the save block in response to the gather command.

In another embodiment, the control unit 420 converts a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL, and uses the converted physical address to convert the stored data information A page corresponding to each of the data corresponding to can be invalidated, and data stored in the invalidated page can be written to the retention block.

In another embodiment, the control unit 420 converts a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL, and uses the converted physical address to convert the stored data When a gather mark is set on a page corresponding to each data corresponding to the information, and garbage collection is performed on a block including the page on which the gather mark is set, the data stored in the page on which the gather mark is set can be written to the retention block. .

In another embodiment, the preservation data information may include a start logical address of data to be stored in the preservation block and the number of target pages.

In another embodiment, when the control unit 420 moves data corresponding to the preservation data information to the preservation block, data corresponding to the number of target pages from the start logical address may be physically stored in the preservation block in a continuous manner.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the embodiments implemented in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (10)

receiving, from a host, a gather command including preservation data information, which is information about data to be stored in a preservation block, which is a block in which data to be preserved is stored; and
moving data corresponding to the stored data information to the storage block in response to the gather command;
A method for improving erase performance of a flash memory storage device, comprising: According to claim 1,
The step of moving to the preservation block is
converting a logical address of a page corresponding to each data corresponding to the preserved data information into a physical address based on a flash translation layer (FTL);
using the converted physical address to invalidate a page corresponding to each data corresponding to the stored data information; and
writing data stored in the invalidated page to the retention block;
A method for improving erase performance of a flash memory storage device, comprising: According to claim 1,
The step of moving to the preservation block is
converting a logical address of a page corresponding to each data corresponding to the stored data information into a physical address based on the FTL;
setting a Gather Mark on a page corresponding to each data corresponding to the stored data information by using the converted physical address; and
when garbage collection (GC) is performed on a block including the page in which the gather mark is set, writing data stored in the page in which the gather mark is set to the retention block;
A method for improving erase performance of a flash memory storage device, comprising: According to claim 1,
The preservation data information is
The method for improving erase performance of a flash memory storage device, characterized in that it includes a start logical address and a target number of pages of data to be stored in the retention block. 5. The method of claim 4,
The step of moving to the preservation block is
and storing the data corresponding to the number of target pages from the start logical address in the retention block so as to be physically contiguous. a receiving unit for receiving a gather command including preservation data information, which is information about data to be stored in a preservation block, which is a block in which the data to be preserved is stored; and
a control unit for moving data corresponding to the storage data information to the storage block in response to the gather command;
A flash memory storage device with improved erase performance comprising a. 7. The method of claim 6,
the control unit
Based on the FTL, the logical address of the page corresponding to each data corresponding to the stored data information is converted into a physical address,
using the converted physical address to invalidate a page corresponding to each data corresponding to the preserved data information,
and writing data stored in the invalidated page to the retention block. 7. The method of claim 6,
the control unit
Based on the FTL, the logical address of the page corresponding to each data corresponding to the preservation data information is converted into a physical address,
setting a gather mark on a page corresponding to each data corresponding to the stored data information by using the converted physical address;
When garbage collection is performed on a block including the page in which the gather mark is set, the data stored in the page in which the gather mark is set is written to the retention block. 7. The method of claim 6,
The preservation data information is
A flash memory storage device with improved erase performance, characterized in that it includes a start logical address and a target number of pages of data to be stored in the retention block. 10. The method of claim 9,
When the control unit moves data corresponding to the preservation data information to the preservation block,
and storing data corresponding to the number of target pages from the start logical address in the retention block so as to be physically contiguous.

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