KR101191320B1 - Apparatus and method for managing flash memory by comparing write data - Google Patents

Abstract

Disclosed are a flash memory management apparatus and method by comparing write data. When the write target data and the address information for storing the write target data are input, the comparison operation unit calculates the differential value data by comparing each bit value of the existing target data and the write target data previously stored in the storage location corresponding to the address information. The compression storage unit compresses the differential data and stores the differential data in a separate storage medium. According to the present invention, by storing the differential data representing only the change bits between the existing data and the data to be written to a separate storage medium, the performance and durability of the flash memory can be improved and the capacity of the storage medium can be efficiently used. .

Description

Apparatus and method for managing flash memory by comparing write data}

The present invention relates to an apparatus and method for managing a flash memory by comparing write data, and more particularly, to an apparatus and method for using a result of comparing data stored as a target to write with data stored in a flash memory write operation. will be.

Flash memory is widely used in portable devices such as digital cameras, MP3 players, mobile phones and PDAs due to the advantages of low power and miniaturization. Recently, as the capacity of flash memory has increased significantly, the tendency to replace disks with flash memory has become common.

Flash memory performs erase-before-write operations because of its physical characteristics.If a write operation is performed on a page, if there is data already stored on the page, the flash memory erases the block to which the page belongs. Write operation can be performed. In order to overcome this drawback, the Flash Translation Layer (FTL), which receives the Logical Page Number (LPN) from the file system, converts it into a Physical Page Number (PPN). Accesses actual flash memory The FTL generates a mapping table for such address translation, and the mapping information is stored in random access memory (RAM).

On the other hand, since flash memory does not support overwriting unlike a hard disk, the write operation requires more time. The overwrite additionally causes garbage collection and merge operations, and the write amplification factor value increases rapidly. In addition, since the flash memory cannot use the block any longer when a certain number of erase operations are performed on the same block, the flash memory should avoid repeating the erase operation on a specific block.

An object of the present invention is to provide an apparatus and method for managing a flash memory by comparing write data which can improve performance of a flash memory based storage device by preventing frequent overwriting.

Another technical problem to be solved by the present invention is a computer that records a program for executing a flash memory management method on a computer by comparing write data, which can improve performance of a flash memory-based storage device by preventing frequent overwriting. To provide a recording medium that can be read by.

According to an aspect of the present invention, there is provided a flash memory management apparatus according to a comparison of write data, comprising: an input unit configured to receive write object data and address information on which the write object data is to be stored; A comparison operation unit which calculates differential value data by comparing each bit value of the data to be written with the existing data previously stored at a storage location corresponding to the address information; A compression storage unit for compressing the differential value data and storing the differential value data in a separate storage medium; And a data erasing unit flushing the differential value data stored in the storage medium to a flash memory in which the existing data is stored, wherein the compressed storage unit writes the write target data when a read request for the write target data is input. And restores and writes the write target data by a comparison operation with the existing data stored in the storage medium, and the data erasing unit accumulates and stores the number of times of use of the differential value data corresponding to the read request. The differential value data stored in the storage medium is flushed in order of decreasing use frequency.

According to an aspect of the present invention, there is provided a method of managing a flash memory by comparing write data, comprising: (a) receiving write target data and address information on which the write target data is to be stored; calculating differential data by comparing each bit value of the data to be written with the existing data previously stored in the storage location corresponding to the address information; (c) compressing the differential value data and storing the differential data; (d) when the read request for the write target data is input, decompressing the differential value data and restoring and outputting the write target data by a comparison operation with the existing data; And (e) accumulating and storing the number of use of the differential value data corresponding to the read request, and flushing the differential value data stored in the storage medium to a flash memory in which the existing data is stored in the order of the smallest number of times of use. Step).

According to the flash memory management apparatus and method by comparing the write data according to the present invention, the performance and durability of the flash memory can be improved by storing the differential value data representing only the change bits between the existing data and the write target data in a separate storage medium. In addition to improving capacity, the capacity of the storage medium can be used efficiently.

1 is a block diagram showing the configuration of a preferred embodiment of a flash memory management apparatus by comparison of write data according to the present invention;
2 is a diagram illustrating an example of calculating differential value data from existing data and write target data;
3 is a flowchart illustrating a process of performing a preferred embodiment of a method of storing information of write target data in a flash memory management method according to the present invention;
4 is a flowchart illustrating an exemplary embodiment of a method of restoring data to be written using differential value data stored in the storage medium 300.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the flash memory management apparatus and method by comparing the write data according to the present invention.

1 is a block diagram showing a configuration of a preferred embodiment of a flash memory management apparatus by comparison of write data according to the present invention.

Referring to FIG. 1, the flash memory management apparatus 100 according to the present invention includes an input unit 110, a comparison operation unit 120, a compression storage unit 130, and a data erasing unit 140, and a flash memory 200. In order to control the write operation for the), a separate storage medium 300 is used.

The input unit 110 receives the write target data and the address information on which the write target data is to be stored, and the comparison operation unit 120 compares each bit value of the existing target data and the write target data previously set at the storage location corresponding to the address information. Differential value data is calculated.

As described above, the flash memory 200 takes a long time for a write operation due to an erase operation before writing, and when the erase operation is performed for a predetermined number of times or more with respect to the same block, the flash memory 200 may no longer use the block. Therefore, in order to solve this problem, the flash memory management apparatus 100 according to the present invention deletes data stored in an address space to perform a write operation when a request for a write operation is input, and then stores write target data in the corresponding address space. Instead, it uses a method of storing information about the data to be written without deleting the existing data. In addition, a separate storage medium 300 for flash memory is used to store information about data to be written.

When the write target data and the address information for storing the write target data are input through the input unit 110, the comparison operation unit 120 stores the existing data and the write target stored in the storage location corresponding to the address information in the flash memory 200. A comparison operation is performed on the data to calculate differential data, which is information about the data to be written.

Preferably, the comparison operation unit 120 may extract a change bit different from the existing data from the write target data by performing an XOR operation on the existing data and the write target data to calculate the differential value data.

2 is a diagram illustrating an example of calculating differential value data from existing data and data to be written. Referring to FIG. 2, when the XOR operation is performed on each of 512 bytes of write target data and each bit value of existing data already stored in the address space where a write operation is to be performed, the differential value data may be divided into the existing data and the write target data. The bit value will have a different number of change bits. In the differential data of FIG. 2, a bit having a value of '1' corresponds to a change bit.

Data that is frequently overwritten in a specific address space may exhibit hot or meta data, in which case the number of change bits in the differential data is small. On the other hand, when the number of change bits of the differential data is large, it is likely that the data corresponds to data that is not frequently overwritten.

The compression storage unit 130 compresses the difference value data calculated in this way and stores the data in the storage medium 300. In this case, the next storage medium 300 may use a next-generation non-volatile memory (NVRAM).

Various researches have already been conducted on hybrid storage using NAND flash memory 100 and NVRAM together. As one of them, a technique for storing the aforementioned FTL mapping table in NVRAM has been proposed.

When the FTL mapping table is managed in a temporary buffer of the flash memory 100, the mapping table must be flushed to the flash memory 100 in preparation for a sudden power failure state. However, the proposed scheme can reduce the additional write operations by storing the mapping table in NVRAM which is frequently overwritten. In addition, if the metadata of the file system is stored in the NVRAM, the metadata may be quickly accessed and the nonvolatile conditions of the metadata may be satisfied, thereby improving performance and durability of the flash memory 200.

Another proposed method is to use NVRAM as a storage medium for hot data by separating hot data that is frequently overwritten and cold data that are not overwritten. In addition, the technique of allowing NVRAM to replace the temporary buffer of the flash memory 200 may prevent the performance degradation that occurs to maintain consistency between the data stored in the flash memory 200 and the data stored in the NVRAM. When the memory 200 is used as an operating system booting device, there is no need to perform additional operations on the flushing command generated by the operating system.

However, the techniques described above do not take into consideration the characteristics of NVRAM, and since NVRAM is not highly integrated as compared to the flash memory 200, the unit capacity per price is very small. That is, since the capacity of the NVRAM is not enough to store the FTL mapping table and the file system metadata, there may be a problem in terms of capacity and price to be used to replace the temporary buffer of the flash memory 200.

The flash memory management apparatus 100 according to the present invention stores only the changed bits of the existing data and the write target data as differential value data as described above in order to fully utilize the small capacity of the NVRAM. Information can be stored.

Meanwhile, the compression storage unit 130 compresses the differential data and stores the differential data in the storage medium 300, that is, the NVRAM, and determines whether to compress the differential data according to the number of changed bits of the differential data. That is, the compression storage unit 130 may compress the differential value data when the number of change bits of the differential value data is smaller than a preset threshold value, and otherwise store the differential value data without compressing the differential value data. Conventional compression methods such as run length encoding may be applied as the compression method of the differential data.

In addition, in the case of differential data having a larger number of change bits than the threshold value, it is highly unlikely to be overwritten frequently. Therefore, the compression storage unit 130 stores the uncompressed differential data as a separate storage medium 300 such as NVRAM. Instead, it may be stored in a temporary buffer of the flash memory 200.

After the write operation is completed by storing the input information of the write target data in the NVRAM as described above, the read operation is performed by comparing the stored write target data with the existing data stored in the flash memory 200.

That is, when the read request for the write target data in which the write operation is completed is input, the comparison operation unit 120 stores the existing data stored in the address information on which the write operation is to be performed and the differential data stored in the storage medium 300, that is, the NVRAM. By comparing the data, the data to be written is restored and output. In this case, since the differential value data stored in the storage medium 300 is compressed by the compression storage unit 130, the compression storage unit 130 decompresses the differential value data corresponding to the write target data when a read request is input. To the comparison operation unit 120. Since the differential value data is obtained by the XOR operation of the existing data and the write target data, the write target data may be restored through the XOR operation of the differential data and the existing data.

On the other hand, when the storage medium 300 is full of compressed differential data, it is necessary to erase it. Accordingly, the data erasing unit 140 stores the number of times that the differential value data is used for each read operation in order to erase the differential value data that is not frequently used among the differential value data stored in the storage medium 300.

When the amount of differential data stored in the storage medium 300 exceeds a certain limit, the data erasing unit 140 selects the differential data having the least number of times of use and selects the page unit, which is a unit of reading and writing of the flash memory 200. Accumulate with. That is, the selected differential value data is stored in the same buffer as one page size of the flash memory 200 in the storage medium 300, and when stored in the buffer, an index is displayed for each differential value data.

When the buffer is filled with the differential value data, the data erasing unit 140 flushes the compressed differential value data stored in the buffer to the flash memory 200. As the differential value data stored in the storage medium 300 is stored in the temporary buffer of the flash memory 200, the mapping table of the flash memory 200 is changed as shown in Table 1 below.

LPN flag index PPN 100 0 One 100 101 0 2 100 102 0 3 100 103 One One 200

In Table 1, if the flag is '0', it indicates compressed differential value data, and if the flag is '1', it indicates uncompressed differential value data. As described above, when the number of change bits of the differential data is larger than the threshold, the differential data may be stored in a temporary buffer of the flash memory 200 without compressing the differential data.

Referring to Table 1, 100, 101, and 102, respectively, different logical page numbers (LPNs) point to the same physical page number (PPN) 100, and index numbers assigned to respective differential data are displayed together in the mapping table.

When overwriting is performed on the compressed differential value data stored in the temporary buffer of the flash memory 200, the data corresponding to the corresponding page is loaded into the storage medium 300, that is, NVRAM.

As described above, the flash memory management apparatus 100 according to the present invention erases existing data already stored from the flash memory 100 to perform a write operation, and instead of storing the write target data, the existing data and the write target. By storing the differential value data representing only the change bits between the data in a separate storage medium 300, the performance and durability of the flash memory 100 may be improved and the capacity of the storage medium 300 may be efficiently used.

3 is a flowchart illustrating a preferred embodiment of a method for storing information of write target data in a flash memory management method according to the present invention.

Referring to FIG. 3, the input unit 110 receives write target data and address information for performing a write operation (S310). The comparison operation unit 120 compares the existing data stored in the location corresponding to the address information of the flash memory 200 with the input write data, that is, performs an XOR operation to calculate differential data (S320). The compression storage unit 130 compresses the calculated differential value data and stores it in a storage medium 300, preferably NVRAM, provided separately (S330). In this case, whether to compress may be determined according to the number of change bits included in the differential data.

4 is a flowchart illustrating an exemplary embodiment of a method of restoring data to be written using differential value data stored in the storage medium 300.

Referring to FIG. 4, when a read request for write target data is input (S410), the compression storage unit 130 is stored at a location corresponding to address information on which write operation has been performed on write target data, that is, write target data. In response to the existing data, the differential value data stored in the storage medium 300 is decompressed, and the comparison operation unit 120 performs an XOR operation on the decompressed differential value data and the existing data stored in the flash memory 200. As a result, the restored write target data is output as a result of the read operation (S430).

FIG. 5 is a diagram illustrating a result of calculating a size of a change bit of differential data by implementing a flash memory management apparatus 200 according to an exemplary embodiment of the present invention, and FIG. It is a graph shown.

In FIG. 5, the size of the change bit is calculated in units of sectors, and the address information of the sector, the number of change bits, and the size of the change bit for the differential data are shown.

In this regard, referring to the graph of FIG. 6, when the size of the change bit is very small (0 to 5%), it may be estimated that metadata is frequently overwritten, and the size of the change bit is 40 to 60%. In case of, it can be assumed that it belongs to general data which is not frequently overwritten. On the other hand, when the size of the change bit is 99 to 100%, it corresponds to a few cases where the bit is inverted due to the influence of the file system.

The present invention can also be embodied as computer-readable codes on a computer-readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission via the Internet) . The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the embodiment in which said invention is directed. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

100-flash memory management
110-input
120-Comparison Operator
130-compressed storage
140-data eraser
200-flash memory
300-storage medium

Claims (15)

An input unit configured to receive write target data and address information for storing the write target data;
A comparison operation unit which calculates differential value data by comparing each bit value of the data to be written with the existing data previously stored at a storage location corresponding to the address information;
A compression storage unit for compressing the differential value data and storing the differential value data in a separate storage medium; And
And a data erasing unit configured to flush the differential value data stored in the storage medium to a flash memory in which the existing data is stored.
When the read request for the write target data is input, the compression storage unit restores and outputs the write target data by a comparison operation with the existing data stored in the storage medium in response to the write target data.
And the data erasing unit accumulates and stores the number of use of the differential value data corresponding to the read request, and flushes the differential value data stored in the storage medium in order of decreasing use count. . The method of claim 1,
And the storage medium is a nonvolatile memory. 3. The method according to claim 1 or 2,
And the comparison operation unit calculates the differential value data by an XOR operation between the existing data and the write target data. delete delete 3. The method according to claim 1 or 2,
The data erasing unit sorts the differential value data stored in the storage medium in the order of the smallest number of times of use, and stores the difference value data in a buffer having a size corresponding to one page of the flash memory. Flash memory management device characterized in that. 3. The method according to claim 1 or 2,
And the compression storage unit compresses the differential value data when the size of the differential value data is smaller than a preset threshold. (a) receiving write data and address information on which the write data is to be stored;
calculating differential data by comparing each bit value of the data to be written with the existing data previously stored in the storage location corresponding to the address information;
(c) compressing the differential value data and storing the differential data;
(d) when the read request for the write target data is input, decompressing the differential value data and restoring and outputting the write target data by a comparison operation with the existing data; And
(e) accumulating and storing the number of use of the differential value data corresponding to the read request, and flushing the differential value data stored in the storage medium to a flash memory in which the existing data is stored in the order of the smallest number of times of use. Flash memory management method comprising a. The method of claim 8,
And the storage medium is a non-volatile memory. 10. The method according to claim 8 or 9,
And in step (b), calculate the differential value data by an XOR operation between the existing data and the write target data. delete delete 10. The method according to claim 8 or 9,
In the step (e), the differential value data stored in the storage medium are sorted in the order of the smallest number of times of use, and stored in a buffer of a size corresponding to one page of the flash memory. Flash memory management method characterized in that the flushing. 10. The method according to claim 8 or 9,
And in step (c), compressing the differential value data when the size of the differential value data is smaller than a preset threshold. A computer-readable recording medium having recorded thereon a program for executing the flash memory management method according to claim 8 or 9.

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