KR20090107309A - Data Writing On a Flash Memory - Google Patents

Abstract

PURPOSE: A flash memory data recording method and a flash memory are provided to record a block where data is recorded or data about whether a page is valid inside the flash memory. CONSTITUTION: A flash memory data recording method comprises the following steps of: setting up a data block area(310) in which data desired by a host is recorded and a log block area(320) in which log data about whether the data block is valid is recorded by a page unit; recording data in the data block area; and recording a log block page corresponding to the log data.

Description

Flash memory data writing method and flash memory {Data Writing On a Flash Memory}

The present invention relates to a flash memory data recording method and a flash memory capable of recording data on whether data written in a flash memory is valid in a flash memory. The internal block of the flash memory is divided into a data recording area and an area in which data relating to validity of recorded data is stored. Accordingly, the present invention relates to a flash memory data recording method and a flash memory capable of confirming whether data written in the flash memory is valid even without a separate memory in addition to the flash memory.

Flash memory is widely used in embedded systems and mobile devices because it has a non-volatile, fast access speed and consumes less power like a hard disk.

In consideration of its hardware characteristics, the flash memory must first perform an operation of erasing the entire block containing the sector in order to perform a write operation on an already written memory sector. However, the number of times that data can be written and erased in one flash memory is limited.

Partial programming is also possible, where data is written to only part of the pages that make up a flash memory block. However, the flash memory of a single-layer cell (SLC) structure has a plurality of write times, such as four or eight times, whereas the flash memory of a multi-layer cell (MLC) structure is limited to one write number.

1 is a flowchart illustrating a method of writing data to a flash memory according to a general method. When an attempt is made to write data on a specific page (S11), it is checked whether the specific page is a page in which data is already recorded (S12). If no data has been recorded or if the page is erased even if it has been recorded, the data is also recorded on the recorded page (S13).

However, if the page has already been recorded, a new page is allocated (S14) and data is recorded in the new page (S15). In addition, information such as a logical address which is called during the operation of the recorded data is recorded in a new page. At this time, in order to distinguish the allocated new page from the previously recorded page, the page obsolete declaration should be made on the previously recorded page.

In the case of a tomographic cell, data relating to the validity of data such as the declaration of invalidation can be recorded in the auxiliary area of the page. However, in the case of the multi-layer cell, the number of times of writing is limited to one, so data regarding validity cannot be recorded again.

Due to this problem, an external nonvolatile memory is additionally installed to manage information on whether data written to the flash memory is valid. When a data read operation is requested to the flash memory, the flash controller accesses information regarding validity stored in the nonvolatile memory. The flash controller reads the data of the page that is recorded as valid based on the accessed information.

However, there is a problem in that the size or cost of manufacturing a flash memory system is increased when a separate nonvolatile memory is added.

According to the present invention, information on the validity of a page or a block in which data is written in the flash memory is stored in the flash memory without adding an external nonvolatile memory. According to the present invention, a predetermined area of an internal block of a flash memory is set as an area in which information on validity of another page or block is stored so that the validity of a predetermined page or block can be confirmed only by the flash memory.

The flash memory data recording method according to the present invention for solving the above problems has at least one block having pages composed of a predetermined number of sectors, and writes data in units of sectors or pages, and in units of blocks. A method of writing data into a flash memory for erasing data, the method comprising: a data block area in which data to be written by a host is written in the block, and log data on whether data blocks in which the data is written are valid are stored in units of pages; Setting a log block area to be recorded; And recording the data in the data block area and recording log data on whether the data block in which the data is recorded is valid in a corresponding log block page.

In the flash memory data reading method according to the present invention for solving the above problems, in the data reading method of the flash memory in which data is recorded according to the above-described writing method, the data is read in each data block according to the log data stored in the log block. Determining whether the recorded data is valid; And reading the data of the data block determined to be valid in the determining step.

The flash memory according to the present invention for solving the above problems has at least one block having a page composed of a predetermined number of sectors, writes data in units of sectors or pages, and erases data in units of blocks. In the flash memory, a data block area in which data to be written by the host is written, and a log block area in which log data about whether the data block in which the data is written is valid is written in units of pages, is set. Data is recorded in the data block area, and log data relating to whether or not the data block in which the data is recorded is valid is recorded in a corresponding log block page.

According to the present invention, data relating to whether a block or page in which data is written to the flash memory is valid is written into the flash memory. Therefore, there is no need to add a nonvolatile memory to the outside. In addition, a block or page in which data is written to the flash memory is grouped into one block to record the data or to manage data regarding its validity. Therefore, it is possible to minimize block or page waste when writing data.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

2 shows the overall structure of a system in which a flash memory operates. The flash controller 100 writes / reads / erases data in the flash memory 400 according to an operation request such as write / read / erase transmitted from the external host 200. The program code memory 300 provides a program code such as a memory access code so that the flash controller 100 can access the flash memory 400 to write / read / erase data.

3 shows the structure of an actual flash memory. As shown, one flash memory consists of 8192 blocks. The block is composed of 32 pages, and one page may be divided into a main region of 512B and an auxiliary region of 16B. In the main area, user data is usually recorded and can be viewed as a set of sectors. In the auxiliary area, information on the validity of data recorded in the main area, ECC, Logical Block Address (LBA), Logical Page Number (LPN), Logical Sector Number (LSN), and erase count are recorded.

FIG. 3 illustrates a small block flash memory in which write / read units of a flash memory and write / read units requested by an external host match. However, the present invention can also be applied to a large block flash memory in which the write / read unit of the flash memory is larger than the write / read unit requested by the external host. In the case of large block flash memory, the main area is composed of four sectors. In large block flash memory, data is recorded in sector units or page units.

Referring to FIG. 4A, the internal block of the flash memory is set to a data block area 310 in which data is written, and a log block area 320 in which data relating to whether the data block 310 is valid is recorded. One example is the illustrated figure. When there are 64 pages in one flash memory block, seven data blocks formed of eight page units exist in the data block area 310. There are eight pages in the log block area 320 in which data relating to the validity of seven data blocks is recorded.

Data blocks are each linked to pages within a log block. When the corresponding block of data is declared invalid in the log block page, an 'Obsolete Flag' is recorded. If any page in the data block is invalidated, the entire data block is invalidated.

Pages within a data block are sequentially assigned page offset numbers. In this embodiment, it is assumed that data is recorded in units of pages. However, the present invention can be applied even when the data recording unit is a sector. All of these belong to the scope of the present invention.

If the data block area and the log block area are set in the flash memory block as shown in (a) to declare the validity of the data block, the memory loss is as much as the log block area. That is, the space in which data to be recorded in the host is recorded by the log block area is reduced. If eight pages are set to one log block, eight of the 64 pages are lost.

(b) shows four pages configured as one data block and one log block. Twelve data blocks exist in the data block area 330 of one flash memory block. Four log blocks exist in the log block area 340. Each data block is linked to a page inside a log block. In the log block page, data relating to validity of a corresponding data block is recorded.

With the structure as shown in (b), if one page is invalidated, three pages remaining in the same data block are invalidated. That is, compared to (a), when one page is invalidated, the number of pages wasted is reduced even if all the data blocks including the page are invalidated.

However, taking the structure as shown in (b), 16 pages of one flash memory block are allocated as log blocks from which data cannot be written from the beginning. Therefore, 16 pages of 64 pages are lost.

Therefore, in order to reduce the loss in the memo due to log block allocation, a predetermined number of pages corresponding to at least two blocks are set to one data block. A description with reference to FIG. 5 is as follows.

When several flash memories FM0 to FM3 are connected to the bus line bus 0, four pages constituting an arbitrary block of each flash memory may be grouped and set as one data block 350. The data block has 16 pages and has a '4 * 4' structure.

Data regarding the validity of the data block grouping the pages corresponding to at least two blocks is recorded in the page P1 in the log block area 360 set in one of the blocks.

In this case, fifteen data blocks each consisting of four pages are set in one flash memory block. One log block consisting of four pages is set.

Thus, memory loss caused by setting log blocks is reduced. While eight pages are lost in FIG. 4A and 16 pages are lost in FIG. 4B, four pages are lost under the structure shown in FIG.

The rate of memory loss caused by setting up log blocks is lower as more flash memory is connected in parallel to the busline. The data block may be configured to have a structure of '2 * 16' or '1 * 64'.

The data block is connected to each page constituting the log block area. In this embodiment, page offsets are assigned to pages constituting the log block area as shown. Each page records data regarding whether data of a data block corresponding to a given page offset number is valid.

As shown in FIG. 5, when data blocks are set in at least two flash memories connected in parallel, data is distributed when the memory is written in one data block. Therefore, it is possible to prevent one flash memory from being intensively accessed and degraded.

FIG. 6 is a diagram illustrating a procedure of giving a page offset to a page constituting a data block when a data block is set in a parallel connected flash memory as shown in FIG. 5.

Rather than sequentially assigning page offsets to pages constituting one flash memory and subsequently assigning page offsets constituting the next flash memory, data is distributed and written to pages constituting parallel-connected flash memory. Give the page offset as shown in 6.

However, as shown in FIG. 6, when a page offset is assigned and a page to be recorded by the host is recorded and data is recorded, only a specific page may be continuously recorded before the entire page is filled.

In this case, a specific page may invalidate the entire data block and eventually increase the rate at which memory is lost. Hereinafter, a description will be given with reference to FIGS. 7 and 8.

FIG. 7 illustrates a page offset accessed when a logical address is called to record data in a host, in the recording order. That is, the page offset called when the host wants to record data is '1-> 2-> 3-> 4-> 4-> 3-> 4'.

FIG. 8 illustrates how data is written to a page as the page offset is called in FIG. 7. As shown in (a), pages constituting one data block are called according to the page offset, respectively, and data is recorded from '1-> 2-> 3-> 4'.

If one attempts to record '4' again, the data block in which data is written in (a) is invalidated. Then, 1, 2, 3 and update data '4' are recorded in another new data block as shown in (b).

If one attempts to record '3' again, the data block in which data is written in (b) is invalidated. Then, 1, 2 and update data '3' and existing data '4' are recorded in another new data block as shown in (c).

If it is desired to record '4' again in this state, the data block in which data is recorded in (c) is invalidated, and 1, 2, 3 and update data '4' are recorded as in (d). That is, if data is to be written again to a page having a page offset in which data is already recorded, the number of invalidated data blocks increases.

Therefore, in order to prevent the data block from being lost when data is not sequentially recorded according to the page offset number, a data block in which data is written may be set regardless of the page offset order. A description with reference to FIG. 9 is as follows.

First, when setting a data block, the main data block in which data to be written by the host is sequentially recorded according to the page offset number assigned to the data block, and the auxiliary data block to be recorded when the data to be recorded in the host is not sequential. Set two types of data blocks.

When data is to be recorded in the host, data is first recorded in the auxiliary data block. When the recorded data reaches a predetermined amount of data, the data is sequentially recorded. If sequentially recorded, the auxiliary data block in which data is recorded is converted into the main data block.

Then, when data is to be recorded in the host, the data is primarily written to the auxiliary data block. However, if the recorded data is not sequential, the auxiliary data block is linked to the main data block. Thus, the updated data is stored in the auxiliary data block, and accessing the main data block can access the updated data stored in the auxiliary data block as linked.

If the data recorded in the auxiliary data block reaches the predetermined data amount, the data is transferred to the new main data block and recorded.

9 is a diagram illustrating a method of recording data using the above-described main data block and auxiliary data block.

As shown in the figure, when data is to be recorded in the host, the data is first recorded in the auxiliary data block B11 as shown in (a). When data is written in four pages, it is checked whether the data written in the auxiliary data block B11 matches the page offset order of the main data block.

In the present embodiment, the data recorded in the auxiliary data block is '1, 2, 3, 4', which corresponds to the page offset order of the main data block. Therefore, the auxiliary data block B11 is replaced with the main data block B21.

In (b), thereafter, the data to be written is recorded in the auxiliary data block B12, and the auxiliary data block B12 is linked to the child blocks of the main data block B22.

When the data recorded in the auxiliary data block B12 in (b) reaches a predetermined amount of data (amount to be written into four pages in this embodiment), the new main data block B23 as shown in (c). Transfer the data by allocating.

10 is a diagram illustrating an example of setting a main data block and an auxiliary data block in a flash memory.

As shown, a predetermined number of pages of the flash memory are collected and set as one main data block 370, an auxiliary data block 380 linked to the main data block 370 is set, and the main data block 370 A log block 390 may be configured, which includes a page for storing data regarding whether the data is valid.

Here, the dotted line indicates the order in which data is written to the page of the auxiliary data block. The auxiliary data block consists of 16 pages in total. When the auxiliary data block is full, the data is replaced with the main data block, or the data is moved to the new main data block, and the data is erased.

The primary data block 370 and the auxiliary data block 380 are linked as indicated by arrows. In addition, data regarding whether the main data block 370 is valid is recorded in the first page of the log block 390.

11 is a diagram illustrating data recorded on a physical page of a main data block and an auxiliary data block according to the present invention.

(a) shows data recorded in the physical page of the main data block. In the main area of the physical page, user data, which is data to be recorded by the host, is recorded. In the auxiliary area of the physical page, data relating to the ECC of the user data, the logical address (LBA) of the main data block, and the linked auxiliary data physical address (secondary PA) are stored. In addition, main block ID data ID is stored so that the corresponding page is a page corresponding to the main data block.

(b) shows data recorded in the physical page of the auxiliary data block. In the main area of the physical page, user data, which is data to be recorded by the host, is recorded. In the auxiliary area of the physical page, an ECC of user data, a physical address (main PA) of a linked main data block, a page offset (main PO) of a main data block in which the user data is to be recorded, and a physical address of the corresponding auxiliary data block ( Auxiliary PA), and the page offset (secondary PO) of the auxiliary data block. In addition, the auxiliary block ID data ID is stored so that the corresponding page is a page corresponding to the auxiliary data block.

Here, the page offset of the auxiliary data block written in the page of the auxiliary data block is the order in which data is written in the corresponding page.

On the other hand, when an operation request is made from the host to the flash memory, the main management table that maps the logical address called by the host and the physical address assigned to the primary data block, the physical address assigned to the auxiliary data block, and the linked primary data block You need an auxiliary management table that maps physical addresses.

The primary management table and the secondary management table should be able to be generated based on the data recorded in the primary data block and the auxiliary data block.

12 shows an example of the main management table (a) and the auxiliary management table (b) used in the present invention. As shown, the primary management table (a) contains a logical address (LBA) used when called by the host, a physical address given to the primary data block (primary physical address), and a physical address assigned to the linked secondary data block (auxiliary). Information about the physical address is stored.

The auxiliary management table (b) includes a physical address (secondary physical address) assigned to an auxiliary data block, an auxiliary page offset (secondary page offset), a physical address assigned to a linked primary data block (primary physical address), and an auxiliary data block. Information about a main page offset, which is a page offset of a main data block to be recorded in the main area of the page, is stored.

In this case, when at least two flash memories are connected to one bus line, the chip enable number CE # is also stored in the auxiliary management table b.

13 is a flow diagram illustrating a method of writing data in a data block and log data in a log block in accordance with the present invention. First, a data block area in which data to be written by the host is to be written in the flash memory, and a log block area in which log data about whether data stored in the data block area is valid is written is set (S21).

If the host wants to record data, the data is recorded in the data block area having a physical address corresponding to the called logical address (S22). Log data on whether the data block is valid is recorded in the log block page corresponding to the data block (S23).

14 is a diagram illustrating a flow of a method of recording data when the data block is set to two types of main data block and auxiliary data block.

As shown, when a logical address is called to record data in the host (S31), the data is recorded in the auxiliary data block (S32). The auxiliary data block is linked to the main data block if there is a main data block to which data has been previously recorded.

On the other hand, it is checked whether the data recorded in the auxiliary data block has reached a predetermined amount of data (S33), and if not, the data is continuously recorded in the auxiliary data block as the logical address is called.

However, if it reaches, it is checked whether the data recorded in the auxiliary data block is sequential (S34). If the recorded data is sequential, the auxiliary data block is replaced with the main data block (S35). Substitution with the main data block is performed by writing ID data stored in the auxiliary area of the page constituting the auxiliary data block as the main block ID data. Writing of ID data of the auxiliary data block page is performed when the data recorded in the auxiliary data block reaches a predetermined amount of data.

After replacing the auxiliary data block with the primary data block, log data regarding whether the data stored in the data block is valid is recorded in the corresponding log block page (S36).

If the auxiliary data block write data that has reached the predetermined data amount is not sequential, the data described in the auxiliary data block is copied to the new main data block, and the auxiliary data block data is erased (S37). Log data of the new main data block is recorded in the corresponding log block page (S36).

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a flowchart showing a method of writing data into a flash memory;

2 is a block diagram showing the structure of a flash memory system of the present invention;

3 is a diagram illustrating a structure of a flash memory to which the present invention is applied;

4 and 5 illustrate examples of setting a flash memory block as a data block area and a log block area according to the present invention;

FIG. 6 is a diagram illustrating a page offset in a data block area of FIG. 5;

7, 8, and 9 illustrate a method of replacing or copying a main data block after writing data to an auxiliary data block according to the present invention;

10 is a diagram illustrating an example of setting a main data block, an auxiliary data block, and a log block in a flash memory block according to the present invention;

11 is a diagram showing a page written in a main data block and an auxiliary data block;

12 is a diagram illustrating a primary management table and an auxiliary management table used in address mapping according to the present invention;

13 and 14 are flow charts showing the flow of a method of writing data to a flash memory according to the present invention.

Claims (29)

10. A method of writing data into a flash memory having at least one block having pages composed of a predetermined number of sectors, writing data in units of sectors or pages, and erasing data in units of blocks. Setting a data block area in which data to be recorded by a host is recorded in the block, and a log block area in which log data about whether the data block in which the data is recorded is valid is written in units of pages; And And recording log data on the validity of the data block in which the data is recorded, in a corresponding log block page. The method of claim 1, The data block area includes a main data block in which data to be written by the host is recorded according to a page offset order, and data which does not conform to the page offset order of the main data block among the data to be recorded is recorded and the main data block is recorded. And an auxiliary data block linked to the flash memory data recording method. The method of claim 2, In the recording step, when data is written to the main data block, The data to be recorded by the host is recorded in the main area of the physical page, and data about the ECC, the main data block logical address, and the linked auxiliary data block physical address of the data recorded in the main area is stored in the auxiliary area of the physical page. And flash memory data recording method. The method of claim 2, In the recording step, when data is written into the auxiliary data block, The data to be recorded by the host is recorded in the main area of the physical page, and the ECC of the data recorded in the main area, the linked main data block physical address, and the data of the main data block in which the data recorded in the main area should be recorded. And data relating to a page offset, a physical address of the auxiliary data block, and a page offset of the auxiliary data block in an auxiliary area of the physical page. The method of claim 4, wherein And a page offset of the auxiliary data block is an order in which data is written in a main area of the physical page. The method of claim 2, The recording step, And ID data indicating whether the block is a main data block or an auxiliary data block in a physical page auxiliary area of the main data block and the auxiliary data block. The method of claim 2, The recording step, Copying data written in the auxiliary data block to the main data block in an offset order of a main data block page; And erasing data recorded in the auxiliary data block. The method of claim 2, A primary management table for mapping a logical address called by the host and a physical address assigned to the primary data block, and a secondary management table for mapping a physical address assigned to the auxiliary data block and a physical address of a linked primary data block; And generating the data based on the data recorded in the data block. The method of claim 8, The main management table includes a logical address called by the host, a physical address of a main data block corresponding to the logical address, and information on a physical address of an auxiliary data block linked to the main data block. How to record data. The method of claim 8, The auxiliary management table includes a physical address assigned to the auxiliary data block, a page offset of the auxiliary data block, a main data block physical address to which the auxiliary data block is linked, and a main data block to which data recorded in the main area is to be recorded. And information about a page offset of the flash memory data. The method of claim 2, The recording step may include recording data to be recorded in the host in the auxiliary data block; Confirming whether data written in the auxiliary data block is written according to a page offset order of a main data block; Replacing the auxiliary data block with the main data block when it is confirmed that the data is recorded in the order in the checking step, and linking the auxiliary data block to the corresponding main data block when it is not confirmed that the data is written in the order. Flash memory data recording method comprising the steps. The method of claim 11, If the data recorded in the auxiliary data block is not confirmed to be recorded in the order in the checking step, when the amount of data recorded in the auxiliary data block reaches a predetermined data amount, Allocating and copying data described in the auxiliary data block to a new main data block; And erasing data described in the auxiliary data block. The method of claim 11, The replacement of the auxiliary data block is performed by recording ID data indicating that the block is a main data block in an auxiliary area of a physical page in which data is recorded in a main area of the auxiliary data block. Way. The method of claim 1, The block area setting step, A predetermined number of pages constituting at least two blocks is set as one data block area, And setting a log block area in which log data of the set data block area is recorded in one of the two blocks. A data reading method of a flash memory in which data is recorded according to the recording method of claim 1, Determining whether data written in each data block is valid according to log data stored in the log block; And And reading data of the data block determined to be valid in the determination step. A flash memory having one or more blocks having pages composed of a predetermined number of sectors, writing data in units of sectors or pages, and erasing data in units of blocks. A data block area in which data desired to be recorded by the host is recorded in the block, and a log block area in which log data about whether the data block in which the data is written is valid is written in units of pages; And writing log data on the validity of the data block in which the data is recorded in the corresponding log block page. The method of claim 16, The data block area includes a main data block in which data to be written by the host is recorded according to a page offset order, and data which does not conform to a page offset order of the main data block among the data to be recorded is recorded and the main data block is recorded. And a secondary data block linked to the flash memory. The method of claim 17, When data is written to the main data block, The data to be recorded by the host is recorded in the main area of the physical page, and data about the ECC, the main data block logical address, and the linked auxiliary data block physical address of the data recorded in the main area is stored in the auxiliary area of the physical page. Flash memory, characterized in that to write to. The method of claim 17, When data is written to the auxiliary data block, The data to be recorded by the host is recorded in the main area of the physical page, and the ECC of the data recorded in the main area, the linked main data block physical address, and the data of the main data block in which the data recorded in the main area should be recorded. And data relating to a page offset, a physical address of an auxiliary data block, and a page offset of an auxiliary data block in an auxiliary area of the physical page. The method of claim 19, And a page offset of the auxiliary data block is an order in which data is written in a main area of the physical page. The method of claim 17, And ID data indicating whether a corresponding block is a main data block or an auxiliary data block in a physical page auxiliary area of the main data block and the auxiliary data block. The method of claim 17, Copy the data recorded in the auxiliary data block to the main data block according to the offset order of the main data block page, And erasing data written to the auxiliary data block. The method of claim 17, A primary management table for mapping a logical address called by the host and a physical address assigned to the primary data block, and a secondary management table for mapping a physical address assigned to the auxiliary data block and a physical address of a linked primary data block; And a flash memory based on data written in the data block. The method of claim 23, The main management table includes a logical address called by the host, a physical address of a main data block corresponding to the logical address, and information on a physical address of an auxiliary data block linked to the main data block. . The method of claim 23, The auxiliary management table includes a physical address assigned to the auxiliary data block, a page offset of the auxiliary data block, a main data block physical address to which the auxiliary data block is linked, and a main data block to which data recorded in the main area is to be recorded. And information about a page offset of the flash memory. The method of claim 17, The data to be recorded in the host is recorded in the auxiliary data block, and the data recorded in the auxiliary data block is checked according to the page offset order of the main data block. Replace the auxiliary data block with the main data block if it is confirmed to be written in the order, and link the auxiliary data block to the corresponding main data block if it is not confirmed to be written in the order. Flash memory. The method of claim 26, If the data recorded in the auxiliary data block is not confirmed to be recorded in the order, if the amount of data recorded in the auxiliary data block reaches a predetermined data amount, And flashing the data described in the auxiliary data block by allocating a new main data block and erasing the data described in the auxiliary data block. The method of claim 26, The replacement of the auxiliary data block is performed by writing ID data indicating that the block is a main data block in an auxiliary area of a physical page in which data is written in a main area of the auxiliary data block. The method of claim 16, Setting a predetermined number of pages constituting at least two blocks into one data block area, and setting a log block area in which log data of the set data block area is recorded to one of the two blocks. Memory.

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