JP7338149B2 - Storage controller and program - Google Patents

Description

The present invention relates to a storage control device and program.

In a flash memory, recorded data cannot be simply rewritten, and new data is written after the recorded data is flushed (in other words, "deleted") in units of blocks.

In the operation of injecting charge into the floating gate and draining it, electrons pass through the oxide film, which is an insulator, so that there is a characteristic that the storage element deteriorates according to writing.

The limit on the number of writes to flash memory is significantly lower than that of a hard disk, and when flash memory is used as a storage medium, consideration is sometimes given not to increase the number of writes.

In order to use flash memory without being restricted by write restrictions, for example, wear leveling is performed so that writing is not concentrated in a specific area, or a certain amount of spare area is reserved in advance to replace defects due to deterioration. Control is performed.

JP-A-10-320984

If a flash memory is provided in place of a hard disk as a storage area that can be rewritten a sufficient number of times, a spare area with a sufficient amount of storage is reserved in advance. As a result, the storage space available to the user can be considerably smaller than the physical flash memory storage space. On the other hand, if the spare area is made smaller, the number of times that data can be written becomes smaller.

It is an object of one aspect of the present invention to effectively utilize a storage area of a semiconductor memory device having a limited number of rewritable times.

A storage control device is a storage control device that controls a semiconductor memory device, and stores all values in a predetermined sector in the continuous bit string in a storage area of the semiconductor memory device that stores data including the bit string. a first write processing unit that writes the data while excluding a predetermined bit pattern of 1; is not rewritten, and the value of the 1-bit rewrite data is 0 for the bit string stored in the area storing the deletable data, the first write maintaining the value in the bit string written by the processing unit, and rewriting the value in the bit string written by the first write processing unit to the predetermined bit pattern when the value of the rewrite data is 1; and a write processing unit.

In one aspect, it is possible to effectively use the memory area of the semiconductor memory device having a limited number of rewritable times.

It is a figure which shows the structural example of the storage apparatus in an example of embodiment. It is a table showing a 3-bit bit pattern. 2 is a table showing bit patterns before additional writing of data used in the storage device shown in FIG. 1; FIG. 2 is a table showing bit patterns after additional writing of data used in the storage device shown in FIG. 1; FIG. 2 is a table showing a first example of write data areas and additional areas in the storage device shown in FIG. 1; 2 is a table showing the types of bit patterns that can be expressed before and after data is additionally written in the storage device shown in FIG. 1; 4 is a table showing a second example of write data areas and additional areas in the storage device shown in FIG. 1; 3 is a table exemplifying a free area bitmap of one block before data is additionally written in the storage device shown in FIG. 1; 3 is a table exemplifying a free area bitmap of one block after data is additionally written in the storage device shown in FIG. 1; 2 is a diagram showing a data conversion table in the storage device shown in FIG. 1; FIG. 2 is a diagram showing an additional data calculation table in the storage device shown in FIG. 1; FIG. 2 is a table showing a record format of a management area in the storage device shown in FIG. 1; 3 is a flowchart for explaining data write processing in the storage device shown in FIG. 1; 3 is a flowchart for explaining data reading processing in the storage device shown in FIG. 1; It is a table which shows an example of the data allocation ratio in a related example. 2 is a table showing an example of data allocation ratios in the storage device shown in FIG. 1;

An embodiment will be described below with reference to the drawings. However, the embodiments shown below are merely examples, and are not intended to exclude the application of various modifications and techniques not explicitly described in the embodiments. In other words, the present embodiment can be modified in various ways without departing from the spirit of the embodiment.

Also, each drawing does not mean that it has only the constituent elements shown in the drawing, but can include other functions and the like.

In the following figures, the same reference numerals denote the same parts, so the description thereof will be omitted.

[A] Example of Embodiment [A-1] System Configuration Example FIG. 1 is a diagram showing a configuration example of a storage device 1 in an example of an embodiment.

The storage device 1 is, for example, a flash memory, and includes a control section 10 and a recording area section 20 .

The recording area section 20 is a semiconductor storage device such as a flash device, and includes a management information area section 21 and a data storage area section 22 .

The management information area section 21 stores information about addressing, information indicating the presence or absence of additional writing, a bitmap, etc. as management information. Details of the management information area section 21 will be described later with reference to FIG. 12 and the like.

The data storage area unit 22 stores actual data. Details of the data storage area section 22 will be described later with reference to FIGS. 5 and 7 and the like.

The control unit 10 may be referred to as a storage control device, and includes, for example, a Central Processing Unit (CPU), a Micro Processing Unit (MPU), a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Programmable Logic Device ( PLD) or Field Programmable Gate Array (FPGA). Also, the control unit 10 may be a combination of two or more types of elements among CPU, MPU, DSP, ASIC, PLD, and FPGA.

The control unit 10 is illustratively a processing device that performs various controls and calculations, and includes a first conversion processing unit 11, a second conversion processing unit 12, a write processing unit 14, a read processing unit 15, a calculation unit 16, a region It functions as a reservation processing unit 17 and an area confirmation processing unit 18 . The control unit 10 also holds a conversion table 13 and a free space bitmap 19 .

In order to realize the functions of the first conversion processing unit 11, the second conversion processing unit 12, the writing processing unit 14, the reading processing unit 15, the calculation unit 16, the area reservation processing unit 17, and the area confirmation processing unit 18, For example, a flexible disk, CD (CD-ROM, CD-R, CD-RW, etc.), DVD (DVD-ROM, DVD-RAM, DVD-R, DVD+R, DVD-RW, DVD+RW, HD DVD, etc.) , Blu-ray disc, magnetic disc, optical disc, magneto-optical disc, or other computer-readable recording medium. Then, the computer (the control unit 10 in this embodiment) may read the program from the above-described recording medium via a reading device (not shown), transfer the program to an internal recording device or an external recording device, and store the program therein. Alternatively, the program may be recorded in a storage device (recording medium) such as a magnetic disk, optical disk, or magneto-optical disk, and provided to the computer from the storage device via a communication path.

When realizing the function of the control unit 10, a program stored in the internal storage device (recording area unit 20 in this embodiment) may be executed by the computer (control unit 10 in this embodiment). Also, a computer may read and execute a program recorded on a recording medium.

The first conversion processing unit 11 converts, for example, data in 14-bit notation into 15-bit notation.

The second conversion processing unit 12, for example, converts data in 15-bit notation into 14-bit notation.

The conversion table 13 is a table used by the first conversion processing unit 11 and the second conversion processing unit 12 for conversion between 14-bit notation and 15-bit notation. Details of the conversion table 13 will be described later with reference to FIG.

The write processing unit 14 writes data to the data storage area unit 22 .

The read processing unit 15 reads data from the data storage area unit 22 .

The calculation unit 16 divides the data before additional writing into 14-bit units. Further, the calculation unit 16 calculates additional data to be added to the data storage area unit 22 .

The area reservation processing unit 17 flushes (in other words, “deletes”) data in a specific area in the data storage area unit 22 to reserve a free area.

The area confirmation processing unit 18 refers to the empty area bitmap 19 to confirm an empty area in the data storage area unit 22 or an area in which additional data can be written. Further, the area confirmation processing unit 18 instructs the area reservation processing unit 17 to flash specific data when the free area or the area in which the additional data can be written is insufficient.

The empty area bitmap 19 indicates an empty area in the data storage area unit 22 or an area in which additional data can be written. Details of the free space bitmap 19 will be described later with reference to FIGS. 8 and 9. FIG.

FIG. 2 is a table showing 3-bit bit patterns.

Assume an n-bit storage unit. The example shown in FIG. 3 shows the case of n=3. Since the number of possible patterns (in other words, "the number of states") for n bits is 2 ⁿ , the number of possible patterns for 3 bits is 2 ³ =8 as shown.

FIG. 3 is a table showing bit patterns before additional writing of data used in the storage device 1 shown in FIG.

Here, as shown in FIG. 3, "state 8" in which all bits are "1" is excluded (see symbol A1), and 2 ⁿ -1=2 ³ -1=7 states are assumed. That is, 2log(7)-bit data can be written as information amount.

FIG. 4 is a table showing bit patterns after additional writing of data used in the storage device 1 shown in FIG.

Assuming that 1-bit data is additionally written without flushing the area in the data storage area 22, when writing, the state in which all bits are 1 is set to "1" (see symbol B1). Other states are set to "0".

FIG. 5 is a table showing a first example of write data areas and additional areas in the storage device 1 shown in FIG.

For example, 4378 bytes are used to record data of 4 kibibytes (KiB) in 3-bit recording units (n=3). That is, in addition to 4096 bytes of write data, 282 bytes are required as an additional area.

FIG. 6 is a table showing the types of bit patterns that can be expressed before and after data is additionally written in the storage device 1 shown in FIG.

When writing and reading, data is converted between 3-bit and 2log(7)-bit representations. Here, as an example, conversion between 15-bit notation and 14-bit notation will be described.

There are 16384 patterns that can be represented by 14 bits (see symbol C1), while there are 7 ⁵ =16807 patterns that can be represented by 15 bits (ie, 3 bits×5) (see symbol C2). In this case, since an extra 1-bit area is required for 14 bits, about 7% of capacity is added.

FIG. 7 is a table showing a second example of write data areas and additional areas in the storage device 1 shown in FIG.

4Kib (ie, 4096 bytes) is 32768 bits, so it fits in 14 bits x 2341. Converting from 14 bits to 15 bits results in 15 bits×2341=35115 bits, which fits in 4390 bits.

Therefore, as shown in FIG. 7, 294 bytes are prepared as an additional area in addition to 4096 bytes of write data. Also, the block size is assumed to be 64 pages (in other words, "sector").

FIG. 8 is a table exemplifying the free area bitmap 19 of one block before data is additionally written in the storage device 1 shown in FIG.

The block shown in FIG. 8 consists of 64 pages.

Before data is additionally written, 4 KiB of data is written to each page. Then, in one example of this embodiment, any three pages that can be deleted (in other words, "trimmed") are used to write one sector of additional data. Since the amount of information for additional write is 1 bit for 3 bits, an area of 12 KiB is required to write 4 KiB of data.

Since one sector of information is written using three pages, the data capacity that can be temporarily provided is reduced, but the reduced data capacity is the spare area of the entire Solid State Drive (SSD) device. can be supplemented with In addition, when the spare area is reduced, a block to which a certain amount of pages has been additionally written, and a block targeted for wear leveling processing may be flushed.

The block shown in FIG. 8 has 30 removable pages. Since one page of information can be additionally written using three pages, ten pages of information can be additionally written without flashing.

FIG. 9 is a table exemplifying the free area bitmap 19 of one block after data is additionally written in the storage device 1 shown in FIG.

In the management information area 21 shown in FIG. 1, information indicating whether additional writing is being performed for each page is stored in 64 bits per block.

Here, in the case of simply recording the pointer to the additional write area increased three times as it is, the address area three times larger is required. However, since a series of additional writes can be stored in a certain close page, recording the next area in the format of how many pages after writing can reduce the area required for address recording.

For example, assuming 64-bit addressing, pointing to the position of "Addendum 9-1" shown in FIG. 9, the next area "Addendum 9-2" is one page later, 3” is recorded as 4 pages later.

4 bits are allocated to information indicating after how many pages subsequent additional data is recorded. The interval from "addition X-1" to "addition X-2" and the interval from "addition X-2" to "addition X-3" are each within 16 pages. Therefore, 64 bits + 4 bits x 2 = 72 bits are used for addressing. On the other hand, simply addressing the entire area results in 64 bits×3=192 bits, and the area used for addressing is greater than 72 bits.

FIG. 10 shows the data conversion table 13 in the storage device 1 shown in FIG.

In the conversion table 13, the original data in decimal number, the original data in binary number of 14 bits, and the converted data in binary number of 15 bits are associated with each other. Conversion from 14-bit notation to 15-bit notation and conversion from 15-bit notation to 14-bit notation are performed using this conversion table 13 .

In the illustrated example, in the original decimal data "7", "14", "21" and "28", "111" is skipped in the converted data so that additional writing can be performed.

That is, the write processing unit 14 functions as an example of a first write processing unit that writes data to the data storage area 22 of the recording area 20 by excluding a predetermined bit pattern in a continuous bit string. Specifically, the write processing unit 14 writes data while excluding a predetermined bit pattern in which all the values in the bit string are "1".

In the example shown in FIG. 10, the length of the bit string is 3 bits separated by periods of the transformed data.

Further, when the data to be read is not additional data, the read processing unit 15 is an example of a first read processing unit that converts the data to be read into the format of original data including a predetermined bit pattern and reads the data. function as

FIG. 11 is a diagram showing a postscript data calculation table in the storage device 1 shown in FIG.

In the postscript data calculation table, when the postscript data is "0", the original write state and the postscript state match. On the other hand, when the additional write data is "1", all bits are "1" in the additional write state regardless of the original write state.

The postscript data calculation table is used to calculate the postscript data.

That is, the write processing unit 14 writes a predetermined bit pattern to the bit string of the area storing the deletable data in the data storage area unit 22, thereby causing the second write processing unit to write additional data. Serves as an example. Specifically, the write processing unit 14 maintains the value in the written bit string when the value of the additional data is "0", and maintains the value in the written bit string when the value of the additional data is "1". Rewrite all the values in the bit string that has been read to "1".

Further, when the data to be read is additional data, the read processing unit 15 is an example of a second read processing unit that reads a group of sectors, which are write units of the additional data, corresponding to the sectors, which are the units of data writing. function as The reading processing unit 15 reads the value of the bit string as "0" when at least one of the values of the bit string is "0", and reads the value of the bit string as "0" when all the values of the bit string are "1". Read the value as "1".

FIG. 12 is a table showing the record format of the management information area section 21 in the storage device 1 shown in FIG.

As shown in FIG. 12, in the management information area 21, 0 to 31 bits are the logical sector address, 32 to 63 bits are the physical sector address, 64 bits are the additional bits, and 65 to 127 bits are spare bits. area.

The data of the logical sector address recognized by the client is written to the physical sector address in the data storage area section 22 .

The write-once bit indicates whether the target data is normal write data or write-once data. Additional data is written in three consecutive sectors.

By writing three sectors of relative address pointer information in the spare area, pages in the discontinuous area can be used as write areas for additional data.

That is, the write processing unit 14 sets the interval between the sectors constituting the sector group, which is the write unit of additional data, corresponding to the sector, which is the unit of data write, in the management information area 21 of the recording area 20. It functions as an example of a second write processing unit that writes.

[A-2] Operation Example A data write process in the storage device 1 shown in FIG. 1 will be described with reference to the flowchart (steps S1 to S12) shown in FIG.

The area confirmation processing unit 18 confirms whether there is an empty area in the data storage area unit 22 (step S1).

If there is an empty area (see Yes route in step S1), the calculator 16 divides the write data into 14-bit units (step S2).

The first conversion processing unit 11 converts the write data from 14-bit notation to 15-bit notation (step S3).

The write processing unit 14 writes the converted data into the data storage area unit 22 (step S4).

The write processing section 14 updates the management information in the management information area section 21 (step S5). Then, the data write processing ends.

In step S1, if there is no free space (see No route in step S1), the area confirmation processing unit 18 confirms whether or not there is a recordable area in the data storage area unit 22 (step S6).

If there is no recordable area (see No route in step S6), the area reservation processing section 17 reserves a free area in the data storage area section 22 (step S7). Then, the process moves to step S2.

In step S6, if there is a recordable area (see Yes route in step S6), the read processing unit 15 reads 3 sectors to be written from the data storage area unit 22 (step S8).

The calculator 16 calculates the write data according to the additional data calculation table shown in FIG. 11 (step S9). That is, in the three sectors to be written, if the additional data is "0", the original write state is maintained, and if the additional data is "1", all bits are changed to "1".

The calculation unit 16 creates postscript data (step S10).

The write processing unit 14 writes additional data to the three sectors to be written in the data storage area unit 22 (step S11).

The write processing unit 14 updates the management information in the management information area unit 21 so that the three sectors to be written have additional bits (step S12). Then, the data write processing ends.

Next, the data read processing in the storage device 1 shown in FIG. 1 will be described using the flowchart (steps S21 to S26) shown in FIG.

The read processing unit 15 confirms the management information in the management information area unit 21 (step S21).

The read processing unit 15 determines whether the read target sector is additional data (step S22).

If the read target sector is not the additional data (see No route in step S22), the read processing unit 15 reads the read target physical sector (step S23).

The second conversion processing unit 12 converts the read data from 15-bit notation to 14-bit notation (step S24). Then, the data reading process ends.

In step S22, if the sector to be read is additional data (see Yes route in step S22), the read processing unit 15 reads 3 sectors as physical sectors to be read (step S25).

The calculation unit 16 calculates the postscript data from the read data according to the postscript data calculation table shown in FIG. 11 (step S26). That is, when any of the three sectors to be read is "0", "0" is calculated as the additional data, and when all the three sectors to be read are "1", "1" is calculated as the additional data. ” is calculated. Then, the data reading process ends.
[A-3] Effect FIG. 15 is a table showing an example of data allocation ratios in related examples. FIG. 16 is a table showing an example of data allocation ratios in the storage device 1 shown in FIG.

In FIGS. 15 and 16, when an ideal wear leveling process is performed, write processes caused by the wear leveling process itself are ignored, and an environment is assumed in which all areas are evenly used. Assume a workload in which 1% of the total capacity is rewritten, 1% is deleted, and 1% is additionally written every day in a situation where 70% of the total capacity including the spare area is used.

In the example shown in FIGS. 15 and 16, 10% of the 70% used is rewritten or deleted relatively frequently, but 60% is data stored for a relatively long period of time. It is unlikely that it will be updated or deleted.

Thus, in the example shown in FIG. 15, 2% of the area is flushed every day by rewriting 1% and deleting 1% of the total capacity.

On the other hand, in the example shown in FIG. 16, when 15 days have passed, there are 30% of pages that can be additionally written. Since one sector of data can be written in three pages, another 10% of data, that is, five days' worth of data can be written without flushing. Then, when there is no additional writeable area, the additional write area is flushed, and a free space is secured by rewriting to a normal write state.

In the related example shown in FIG. 15, after 20 days, 40% of the area needs to be flashed. On the other hand, in the example embodiment shown in FIG. 16, after 20 days, 30% of the area may be flushed.

As a result, in one example embodiment, fewer flashes can extend the life of the device by about 33% compared to the related example.

According to the control unit 10 of the storage device 1 in the example of the embodiment described above, for example, the following effects can be obtained.

The write processing unit 14 writes data to the data storage area 22 of the recording area 20 while excluding a predetermined bit pattern in the continuous bit string. The write processing unit 14 also writes postscript data by writing a predetermined bit pattern to a bit string in an area storing deletable data in the data storage area unit 22 .

This makes it possible to effectively use the memory area of the semiconductor memory device, which has a limited number of rewritable times.

The write processing unit 14 writes data while excluding a predetermined bit pattern in which all the values in the bit string are "1". The write processing unit 14 maintains the value of the written bit string when the value of the additional data is "0", and maintains the value of the written bit string when the value of the additional data is "1". Rewrite all values to "1".

As a result, it is possible to reliably write the additional data.

The write processing unit 14 writes, in the management information area section 21 of the recording area section 20, the interval between the sectors that constitute the sector group that is the write unit of the additional data corresponding to the sector that is the write unit of data.

As a result, additional data can be written even if the sectors to be additionally written are not continuous. In addition, the amount of information for specifying the writing position of the additional data can be reduced compared to the case where the addresses of all the additional data are held.

When the data to be read is not additional data, the read processing unit 15 converts the data to be read into a format including a predetermined bit pattern and reads the data.

As a result, it is possible to reliably read data without additional data.

When the data to be read is additional data, the read processing unit 15 reads the sector group, which is the write unit of the additional data, corresponding to the sector, which is the data write unit. Further, the reading processing unit 15 reads the value of the bit string as "0" when at least one of the values of the bit string is "0", and reads the value of the bit string as "0" when all the values of the bit string are "1". Read the value of the bit string as "1".

As a result, the additional data can be reliably read.

[B] Others The technology disclosed herein is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the embodiments. Each configuration and each process of this embodiment can be selected or discarded as necessary, or may be combined as appropriate.

[C] Supplementary Notes Regarding the above embodiment, the following supplementary notes are disclosed.

(Appendix 1)
A storage control device for controlling a semiconductor memory device,
a first write processing unit that writes data in a continuous bit string excluding a predetermined bit pattern to a storage area of the semiconductor memory device;
a second write processing unit that writes additional data by writing the predetermined bit pattern to the bit string in the area storing deletable data in the storage area;
A storage controller, comprising:

(Appendix 2)
The first write processing unit writes data by excluding the predetermined bit pattern in which all the values in the bit string are 1,
The second write processing unit maintains the value in the bit string written by the first write processing unit when the value of the additional data is 0, and maintains the value in the bit string written by the first write processing unit when the value of the additional data is 1. Rewriting all the values in the bit string written by the first write processing unit to 1;
The storage control device according to appendix 1.

(Appendix 3)
The second write processing unit configures a sector group, which is a write unit of additional data, corresponding to a sector, which is a data write unit by the first write processing unit, in the management area of the semiconductor storage device. write the interval of sectors,
3. The storage control device according to appendix 1 or 2.

(Appendix 4)
Further comprising a first reading processing unit that, when the data to be read is not the additional data, converts the data to be read into a format containing the predetermined bit pattern and reads the data;
The storage control device according to any one of Appendices 1 to 3.

(Appendix 5)
When the data to be read is additional data, the sector group corresponding to the sector, which is the data writing unit by the first writing processing unit, is read as the writing unit of the additional data in the second writing processing unit. 2 further comprising a reading processing unit,
The second reading processing unit reads the value of the bit string as 0 when at least one of the values of the bit string is 0, and reads the value of the bit string as 0 when all the values of the bit string are 1. reads as 1,
The storage control device according to any one of Appendices 1 to 4.

(Appendix 6)
A computer that controls a semiconductor memory device,
writing data to a storage area of the semiconductor memory device while excluding a predetermined bit pattern in a continuous bit string;
writing additional data by writing the predetermined bit pattern to the bit string in the area storing deletable data in the storage area;
A program that executes a process.

(Appendix 7)
writing data by excluding the predetermined bit pattern in which the values in the bit string are all 1;
When the value of the additional data is 0, the value in the written bit string is maintained, and when the value of the additional data is 1, all the values in the written bit string are rewritten to 1;
7. The program according to appendix 6, causing the computer to execute a process.

(Appendix 8)
writing, in the management area of the semiconductor storage device, an interval between each sector constituting a sector group, which is a write unit of additional data, corresponding to a sector, which is a write unit of data;
8. The program according to appendix 6 or 7, causing the computer to execute a process.

(Appendix 9)
If the data to be read is not the additional data, the data to be read is converted into a format containing the predetermined bit pattern and the data is read.
9. The program according to any one of Appendices 6 to 8, which causes the computer to execute a process.

(Appendix 10)
If the data to be read is the additional data, read the sector group that is the writing unit of the additional data corresponding to the sector that is the writing unit of the data,
reading the value of the bit string as 0 if at least one of the values of the bit string is 0, and reading the value of the bit string as 1 if all the values of the bit string are 1;
10. The program according to any one of Appendices 6 to 9, which causes the computer to execute processing.

1: Storage device 10: Control unit 11: First conversion processing unit 12: Second conversion processing unit 13: Conversion table 14: Write processing unit 15: Read processing unit 16: Calculation unit 17: Area reservation processing unit 18: Area confirmation Processing unit 19: Empty area bitmap 20: Recording area unit 21: Management information area unit 22: Data storage area unit

Claims (4)

A storage control device for controlling a semiconductor storage device having a storage area for storing data ,
A plurality of bit strings having a bit length of n bits (n is an integer equal to or greater than 3) are concatenated, and the original binary data corresponding to the original data in decimal is converted from 1 bit to n−1 of the original binary data. A first write operation for writing the post-conversion data into the storage area, the post-conversion data being converted such that the bit string does not include a bit string whose values are all 1 when converting to the post-conversion binary data having an overall bit length with more bits. a processing unit;
A second write operation in which 1-bit rewrite data is written using the bit string having a bit length of n bits to the post-conversion data stored in an area indicating that erasure is possible in the storage area. a processing unit;
with
The second write processing unit maintains the value of the post-conversion data written by the first write processing unit when the value of the rewrite data is 0, and maintains the value of the post-conversion data written by the first write processing unit when the value of the rewrite data is 1. rewrites the values in the post-conversion data written by the first write processing unit to a bit string of all 1 values,
Storage controller . When the data to be read stored in the storage area is not the rewriting data, the first reading processing unit converts the data to be read into a format including a bit string in which all the values are 1 and reads the data. further comprising
The storage control device according to claim 1 . When the data to be read stored in the storage area is the rewriting data, a second reading processing unit that reads each of the plurality of concatenated bit strings having a bit length of n bits ,
In each of the plurality of concatenated bit strings having a bit length of n bits, the second reading processing unit sets the value of the bit string to 0 when at least one of the values of the bit strings constituting the bit string is 0. While reading , if the values of the bit string constituting the bit string are all 1, the value of the bit string is read as 1;
3. The storage control device according to claim 1 or 2 . A computer that controls a semiconductor memory device having a memory area for storing data including bit strings ,
A plurality of bit strings having a bit length of n bits (n is an integer equal to or greater than 3) are concatenated, and the original binary data corresponding to the original data in decimal is converted from 1 bit to n−1 of the original binary data. writing the post-conversion data into the storage area, the post-conversion data being converted such that the bit string does not include a bit string whose values are all 1 when converted into post-conversion binary data having an overall bit length of more bits;
writing 1-bit rewrite data using the bit string having a bit length of n bits to the post- conversion data stored in an area indicating that deletion is possible in the storage area;
When the value of the rewrite data is 0, the value of the written post-conversion data is maintained, and when the value of the rewrite data is 1, all the values in the written post-conversion data are maintained. Rewrite to a bit string with a value of 1,
A program that executes a process.

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