KR101375832B1 - Data storage system and data management method - Google Patents

Abstract

The present invention includes a flash memory in which data is stored; And a phase change random access memory (PCRAM) in which update contents of the data are sequentially stored in an order of occurrence, wherein the update contents are updated when data stored in the flash memory is updated in an upper memory. It provides a data storage system that is the difference between all data and updated data.

Description

TECHNICAL FIELD [0001] The present invention relates to a data storage system and a data management method,

The present invention relates to a data storage system, and more particularly, to a data storage system and a data management method using a flash memory and a phase change memory.

Flash memory-based storage devices are popular because they have faster read / write speeds than conventional disk storage devices. For example, in the table of FIG. 3, which compares the speed difference of various storage media, the disk takes 12.7 milliseconds to read and 13.7 milliseconds to write 2KB of data, while NAND flash memory. The access time for the same amount of data is only 75 microseconds for read and 250 microseconds for write, which is much faster.

Flash memory, however, has several drawbacks. For example, as shown in the table, unlike a hard disk, a flash memory must first delete the data before storing the data. The read / write operation of the flash memory is performed by page unit rather than byte unit, and data deletion operation should be performed by block unit. Since these operations deteriorate each time, excessive data updates reduce the lifespan of the flash memory.

Therefore, efforts have been made to improve the performance of flash memory by circumventing these shortcomings such as various methods of flash translation layer (FTL).

On the other hand, Phase Change Random Access Memory (PCRAM), a next-generation nonvolatile memory, enables random writes in bytes, and there is no restriction that data must be deleted first for data update. Shows read performance.

However, there are drawbacks to phase-conversion memory, so using flash memory and phase-conversion memory together to complement each other can create data storage systems and data management methods that provide better performance than single-use.

In this regard, Korean Patent Registration No. 10-2010-0037789 ("memory device and a management method of a memory device") discloses a configuration in which a data block for storing data and a log block for storing updated values of the data are disclosed.

In addition, Korean Patent No. 10-2010-0057346 ("memory device and a method of operating the memory device") includes a flash memory and NVRAM, NVRAM is a sequential write if the data size of the write command is larger than the threshold, random if the threshold is below The writing configuration is disclosed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a data storage system and a data management method that provide improved performance by complementary complementary flash memory and phase change memory.

A data storage system according to the first aspect of the present invention for achieving the above object includes a flash memory in which data is stored; And a phase change random access memory (PCRAM) in which update contents of the data are sequentially stored in an order of occurrence, wherein the update contents are updated when data stored in the flash memory is updated in an upper memory. It is characterized in that the difference between the previous data and the updated data.

A data management method using a data storage system including a flash memory and a phase change memory according to the second aspect of the present invention for achieving the above object includes (a) the phase change memory in the data stored in the flash memory; Loading data to which the update contents are stored in the upper memory; (b) storing updated contents of the data loaded and updated in the upper memory in the phase change memory; And (c) updating the data stored in the flash memory by merging the update contents stored in the phase change memory with the data stored in the flash memory, wherein the update contents are data stored in the flash memory. When is updated in the upper memory is characterized in that the difference between the data before the update and the updated data.

The present invention achieves the effect of improving performance by configuring the flash memory and the phase change memory to complement each other in the data storage system and the data management method.

Specifically, when updating data, instead of accessing the flash memory where the data is stored, the contents of the data are stored in the phase conversion memory and the flash memory data is reduced, thereby improving the random writing speed of the flash memory. Get

The high speed of writing small amount of data in the phase conversion memory can be utilized, and the data storage time is shorter than storing the update contents in the log area of the flash memory.

Since the number of flash memory data updates is reduced, the disadvantage of flash memory, which must be erased first for writing and a large amount of data must be written / deleted at a time, avoids the deterioration of the area storing frequently updated data. This can prevent the flash memory from shortening its lifespan.

In addition, since the log area is not fixedly allocated to each page in the phase change memory, the utilization of the phase change memory space is high, the load due to the mapping is low, and deterioration is increased in a specific area, thereby preventing the life of the phase change memory from being shortened. .

In addition, because it does not require complex operations, resource utilization is efficient, good performance, and easy to implement.

1 and 2 show a data storage system according to the invention.
3 shows a comparison of the speed differences of various storage media.
4 illustrates a flow of a data management method according to the present invention.
Figure 5 shows the flow of the data loading step into the main memory of the data management method according to the present invention.
Figure 6 shows the flow of the update content storing step to the phase change memory of the data management method according to the present invention.
Figure 7 shows the flow of the update content merging step into the flash memory of the data management method according to the present invention.
8 shows a state before data is loaded into the main memory in the embodiment of the data storage system according to the present invention.
9 is a diagram illustrating a process of loading and updating data into a main memory in an embodiment of a data storage system according to the present invention.
FIG. 10 illustrates a state in which updates are stored in a phase conversion memory in an embodiment of a data storage system according to the present invention. FIG.
11 illustrates a state in which update contents are merged into a flash memory in an embodiment of a data storage system according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between . Also, when an element is referred to as "comprising ", it means that it can include other elements as well, without departing from the other elements unless specifically stated otherwise.

1 shows a data storage system according to the invention.

The data storage system 10 according to the present invention includes a flash memory 100, which is a nonvolatile storage medium for storing data, and a phase change memory 200, which is a nonvolatile storage medium for storing update contents of data.

There is no limitation on the configuration of the data storage system 10 according to the present invention. For example, in one embodiment, the flash memory 100 may be configured in the form of a solid state disk (SSD), and the phase change memory 200 may be configured in the form included in the SSD. Alternatively, the flash memory 100 and the phase change memory 200 may be configured independently of each other. In addition, there is no limitation on the type, number and capacity of the flash memory 100 and the phase change memory 200. The data storage system 10 may also be used in connection with other auxiliary storage devices such as a hard disk.

Data stored in the data storage system 10 is loaded into an upper memory such as main memory (RAM) and used. In an exemplary embodiment, the main memory may include a dedicated buffer 20 for reading and using data stored in the data storage system 10, more specifically, a data area 300 in the buffer 20. In addition, the main memory buffer 20 may further include a log area 400 for storing updated contents when data loaded in the data area 300 is updated.

2 shows an internal structure of a data storage system according to the present invention.

Data is stored in the flash memory 100. As described above, the flash memory 100 reads and writes data in units of pages rather than bytes, and data erasing is performed by a block unit that is a set of pages. For example, each page has a capacity of 2 KB, and each block may consist of 32 pages.

As shown in the figure, if the i-th block of the flash memory 100 is Bi and the j-th page of each block is Pj, the j-th page of the i-th block may be represented as BiPj. Where BiPj is a logical address, not a physical address. Details will be described later through examples.

The phase change memory 200 stores update contents of data stored in the flash memory 100. The update content is a difference between the data before updating and the updated data when the data is loaded into the upper memory (main memory) and updated, and may be referred to as difference data or log. That is, the update content may be defined as the difference between the pre-update version and the post-update version of the data.

This update is stored in the phase-change memory 200. Since the phase change memory 200 fixedly allocates the update content storage space for each block of the flash memory 100, the phase change memory 200 is applied to pages belonging to the i th block Bi of the flash memory 100. The update storage space allocated to may be represented as Li. For example, update contents of the first page B1P1 and the second page B1P2 of the first block of the flash memory 100 are all stored in the first update storage space L1 of the phase-change memory 200. do.

That is, the phase change memory 200 does not allocate the update content storage space for each page of the flash memory 100. The reason why the phase change memory 200 allocates the update content storage space for each block will be described in detail later.

As described above, the data stored in the flash memory 100 is loaded into the buffer 20 provided in the main memory. In one embodiment, the data area 300 of the main memory buffer 20 stores data in a log area. 400 is configured to store the update contents of the data. Since data is stored in the flash memory 100, the data unit loaded into the data area 300 of the main memory buffer 20 is a page. On the other hand, the unit in which the loaded data is updated is bytes, and typically only a fraction of the entire page is changed. For example, when applied to a database system, it is known that the data updated by a database operation is only an average of tens of bytes.

Considering that the page unit of a flash memory medium is usually larger than 2 KB and its capacity is becoming larger, the entire page is updated by accessing the flash memory 100 in order to apply the update content of only a few tens of bytes. Overwriting is very inefficient and has several disadvantages. As described above, the flash memory 100 may perform a write operation in units of blocks and then perform a write operation in units of pages, so that data may be updated so that changes of tens of bytes are applied, thereby further degrading performance. There is also a problem in that the memory life is reduced every time a degradation occurs.

The data storage system 10 according to the present invention effectively solves the above-mentioned problems by collecting the update contents in the phase conversion memory 200 without immediately updating the data stored in the flash memory 100 when the data is updated. Solve. The phase change memory 200 is a non-volatile storage medium capable of writing in bytes, showing a write speed close to DRAM for small amounts of data, and eliminating the need to perform a deletion before writing. Therefore, the phase change memory 200 is suitable for storing update contents. .

For example, if 2 KB of B1P1 data is loaded in the data area 300 of the main memory buffer 20, and 70 bytes of this page are changed by the database operation and 32 bytes are changed again, the phase change memory ( It is only necessary to sequentially record the update contents of 70 bytes and the update contents of 32 bytes in the L1 area of 200).

In this way, when data is needed, the latest version of the data can be calculated using the record of the update contents when the data is needed without updating the data in the flash memory 100. This is an operation performed when data is loaded into the data area 300 of the main memory buffer 20. For example, after reading the data from the flash memory 100, the updated contents are read from the L1 region of the phase conversion memory, 70 bytes of updated contents are applied, and 32 bytes of updated contents are applied again.

Whenever there is a read request, the cost of going through this latest version reconstruction process is low compared to the advantages such as a significant improvement in write speed as described above. This is because the phase-change memory reads the update content because the read speed of the small amount of data is also fast. Consideration of the trade-offs for faster write speeds and slower read speeds will be discussed later.

Accordingly, the data storage system 10 according to the present invention appends and stores the updated contents in the order of occurrence when the updated contents are stored in the phase conversion memory 200. This is a characteristic that has several advantages. Since there is no fixed size and position for each page, there is no computational load such as mapping. There is also no problem of deterioration in a particular area. Even if the end-of-life cell is a part of the entire memory, the entire memory cannot be used. Therefore, when using a storage medium that exhibits a deterioration phenomenon in which the life of the memory cell decreases every time the flash memory 100 or the phase change memory 200 is used. It is desirable to be careful not to deteriorate the specific area, but the data storage system 10 according to the invention has this advantage.

In addition, since the update contents are simply added to the end of the previously stored data and do not require any special operation, the update contents are collected in the log area 400 of the main memory buffer 20, and the phase conversion memory is stored at once. It becomes possible to write to 200. In such an embodiment, since I / O operations are further reduced, the performance may be further improved.

However, as described above, the data storage system 10 according to the present invention does not allocate the update contents storage space of the phase change memory 200 fixedly for each page, but fixedly for each block. Although fixed allocation for each page is not preferable because of the above-mentioned reasons, it is preferable to divide by page unit by block rather than using the entire phase-transform memory 200 without any division. For example, if you simply store the update contents sequentially from the beginning of the medium without block division, you will suffer from the above-mentioned deterioration weighting problem.

More importantly, there arises a problem that the above-described read speed decreases. For example, if there are 2 updates for B1P1, 1 update for B1P2, 3 updates for B2P1, 1 update for B3P5, and 2 updates for B3P7, If all of these updates are stored sequentially in order of occurrence without block division, a total of 9 updates must be read to return the latest version of B1P1. This means that not only speed, but also the required temporary memory space can be increased. On the other hand, in case of storing by dividing by block, it is efficient because only 3 update contents need to be read.

That is, the main reason why the data storage system 10 according to the present invention fixedly allocates an area for storing update contents on a block basis is a trade-off between read and write. Accordingly, the allocation area threshold for each block may be set. Assuming that the page size of the flash memory 100 is 2KB, the number of pages per block is 32, and the read and write frequencies are the same, the read burden of the phase-conversion memory 200 = (differential data area size / 2/32) * Read speed, write burden = write speed. When calculating by applying the read speed and the write speed shown in FIG. 3, it is concluded that the difference data area size is approximately 2 KB or less.

Since the update content storage space is fixedly allocated for each block, an update content storage space in which data cannot be stored anymore may be generated because the data is full. In this case, the data stored in the flash memory 100 of the block is updated to the latest version, and the corresponding update contents storage space of the phase change memory 200 may be emptied. That is, the update of the data stored in the flash memory 100 is made at this point.

4, 5, 6, and 7 show the flow of the data management method according to the present invention.

4 shows the overall flow.

When the j-th page (BiPj) data of the i-th block Bi of the flash memory 100 to be loaded into the main memory buffer 20 is requested (S410), the contents of the request page (BiPj) stored in the flash memory 100 Of the update contents stored in the update contents storage space (Li) allocated to the corresponding block (Bi) of the conversion memory (200), the data of the best version in which the updates to the request page (BiPj) are sequentially applied are returned. In operation S420, the data memory 300 is loaded into the data area 300 of the main memory buffer 20.

When the page BiPj is updated in the main memory buffer 20 (S430), the update contents are recorded in the log area 400 of the main memory buffer 20 (S440), and the log area 400 is full or the checkpoint is updated. When it is necessary to write the update content data in the nonvolatile storage device for reasons such as an operation (S450), the page BiPj original data stored in the flash memory 100 is not updated, but the phase-conversion memory 200 is instead updated. The update content is stored in the update area storage space Li of the device (S460). At this time, as described above, the data is stored in addition to the update contents data previously stored in the order of occurrence without overwriting.

When the update area storage space Li of the phase conversion memory 200 is full and a need to merge the update contents with the original data of the flash memory 100 occurs (S470), the corresponding block Bi of the flash memory 100 is generated. The original data of the flash memory 100 is a latest version calculated by sequentially merging the update contents of the corresponding page stored in the update contents storage space Li of the phase conversion memory 200 with the original data of each page belonging to. Is updated and the corresponding area Li of the phase conversion memory 200 is emptied (S480).

FIG. 5 shows the flow of the data loading step (420 in FIG. 4) into the main memory of the data management method according to the present invention.

The original data of the page requested to be read (BiPj) is read from the flash memory 100 (S510), and in the update content storage space Li allocated to the block Bi belonging to the page in the phase conversion memory 200. If all stored update contents are read (S520), and only the update contents of the corresponding read request page BiPj are sequentially applied to the original data read in step S510 (S530), the corresponding page (BiPj) data Is reorganized into the latest version, so you can return it.

Fig. 6 shows the flow of the update contents storing step (460 of Fig. 4) to the phase change memory of the data management method according to the present invention.

The update contents of the write request page BiPj are all stored in the update contents storage space Li allocated to the block Bi to which the write request page BiPj of the phase-change memory 200 belongs (S610). At this time, as described above, it is stored without being overwritten. As described above, the original data stored in the flash memory 100 of the write request page BiPj is not updated at this time. Instead of updating the data source every time, the data management method according to the present invention achieves various effects as described above. The flash memory 100 is complemented by using a phase change memory 200, which is a medium more suitable than the flash memory 100 for storing update contents.

7 shows the flow of the update content merging step (480 of FIG. 4) of the data management method according to the present invention.

First, an empty block is allocated to the flash memory 100 (S710).

After all the update contents are read from the update contents storage space Li of the merge required block Bi of the phase-conversion memory 200 (S720), until all pages of the merge required block Bi are updated (S750). ) Update contents of the corresponding page are sequentially applied to each page of the block (S730), and the page updated with the latest version is recorded in the allocated empty block (S740).

The block mapping information is changed in the flash memory 100 and the previous block is returned as an empty block (S760).

In this case, since each page of the corresponding block Bi of the flash memory 100 has been updated and stored as the latest version, it is no longer necessary to maintain the existing update contents, so that the update contents storage space for the corresponding block of the phase conversion memory 200 ( Li) can be used again from the beginning.

8, 9, 10 and 11 show an embodiment of a data storage system according to the invention.

For convenience, the logical block number of the flash memory 100 is limited to two and the number of pages per block is limited to two. Each page may be represented by a logical address BiPj as described above. For example, B2P2 is logically the second page of the second block.

The version of each page data is represented by _ followed by the number of times it has been loaded in main memory and updated. For example, B2P2_0 is the original version stored logically in the flash memory 100 of the second page of the second block. Here, the original data is data before being loaded into the main memory buffer 20 and updated, that is, the number of updates is 0, and there is no update content to be stored in the phase conversion memory 200.

The phase change memory 200 allocates update content storage space for each block. In the present embodiment, since the number of blocks of the flash memory 100 is two, the number of update contents storage space provided in the phase conversion memory 200 is two. That is, L1 and L2 of the phase change memory 200 are update content storage spaces corresponding to blocks B1 and B2 of the flash memory 100, respectively.

The update content is the difference between the pre-update and post-update versions of the updated data after being loaded into the main memory buffer 20. Since the update contents are sequentially stored in the allocated space for each block, the update contents storage space number and occurrence Let's use numbers. For example, L1D1 is the first update content to be stored in the first update content storage space L1.

8 illustrates a state before data is loaded into the main memory in the embodiment of the data storage system according to the present invention.

Since it is in the state before loading and updating to main memory, the flash memory 100 stores B1P1_0, B1P2_0, B2P1_0, and B2P2_0, which are the original data of each page, and stores the update contents storage space L1, of the phase change memory 200. L2) is empty.

9 is a diagram illustrating a process of loading and updating data into a main memory in an embodiment of a data storage system according to the present invention. The state of the phase change memory 200 after the process of FIG. 9 is illustrated in FIG. 10.

When the data page is loaded into the main memory, the data storage system 10 according to the present invention applies the update contents stored in the phase conversion memory 200 to the original data stored in the flash memory 100 as described above. Reconstruct and return the latest version.

Accordingly, in the first state diagram of FIG. 9, B2P1_0, which is the first page data of the second block of the flash memory 100, is loaded into the data area 300 of the main memory buffer 20. Currently there is no updated content, so only the original in the flash memory 100 needs to be loaded.

In the second state diagram, the above page data B2P1_0 has been updated to the B2P1_1 version. The update content L2D1 at this time is a difference between B2P1_0 which is a version before update and B2P1_1 which is a version after update. In the drawings, it is shown using a minus sign for convenience. As described above, L2D1 is the first update content to be stored in the L2 area of the phase change memory 200. Updated page B2P Since the page belongs to the second logical block B2, the update contents for this page are stored in L2.

In the third state diagram, the B1P1_0 data has been loaded. As in the first state drawing, the original data is loaded as there is no update to be applied at load.

In the fourth state diagram, the page data B1P1_0 has been updated to the B1P1_1 version. The update content L1D1 is a difference between B1P1_0 which is a version before update and B1P1_1 which is a version after update.

In the fifth state diagram, the page data B2P1_1 has been updated to the B2P1_2 version. That is, the page B2P1 has been updated a second time after being loaded into the main memory buffer 20. The update content is the second update content to be stored in the L2 area of the phase-change memory 200 and may be referred to as L2D2.

The B1P2_0 data was loaded in the sixth state diagram and updated to the B1P2_1 version in the seventh state diagram. The update content is L1D2 since it is the second data of the update content to be stored in L1.

In the eighth state figure, the page data B2P1_2 has once again been updated to the B2P1_2 version. The update is L2D3 since it is the third update to be stored in the L2 area of the phase-change memory 200.

In summary, as shown in the drawing, the update content is the difference between the pre-update and post-update versions of the updated page, and is stored in the order of occurrence regardless of the page order in the update content storage space corresponding to the block to which the page belongs. .

10 illustrates a state in which an update is stored in a phase conversion memory in an embodiment of a data storage system according to the present invention.

The update contents generated in FIG. 9 are stored in the update contents storage area. As shown, the size of the update contents is not fixed. In the L1 area, only two updates are stored, but they are full. In the L2 area, empty space remains even though three updates are stored.

11 illustrates a state in which update contents are merged into a flash memory in an embodiment of a data storage system according to the present invention.

Since L1 of FIG. 10 is full and there is no more space for storing the updated contents, it should be empty. As described above, this is the time when the original data of the flash memory 100 is updated.

As shown, first, an empty block of the flash memory 100 is newly allocated to B1. That is, B1, which is logically the first block, is physically allocated from the first block to the third block.

After all of the update contents L1D1 and L1D2 are read from the update contents storage space L1 of the corresponding block of the phase conversion memory 200, the corresponding update contents are applied to each page belonging to the block and stored in the newly allocated block. That is, the first page is merged into the latest version reconstructed by applying L1D1 to the original data B1P1_0, and the second page is merged into the latest version reconstructed by applying L1D2 to the original data B1P2_0. Since the merged data becomes the version before it is loaded into the main memory and updated, it becomes the original data B1P1_0 and B1P2_0 by definition. That is, the B1P1_0 and B1P2_0 data shown in FIG. 10 are different from the B1P1_0 and B1P2_0 shown in FIG. 8.

Since the data has been merged with the flash memory 100, the update content data in the L1 region of the phase change memory 200 is no longer needed. Therefore, it is only necessary to save the update contents data such as L1D1 and L1D2 which are newly generated from the beginning again by emptying the corresponding area.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is shown by the following claims rather than the above description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

10: Memory system
100: flash memory
200: phase change memory

Claims (18)

In a data storage system,
A flash memory in which data is stored; And
And a phase change memory (PCRAM: Phase Change Random Access Memory) in which the updated contents of the data are sequentially stored in the order of occurrence.
The update content is a difference between the data before the update and the updated data when the data stored in the flash memory is updated in the upper memory,
And updating content storage space of the phase change memory is allocated for each block of the flash memory. The method of claim 1,
When the data is requested, the data storage system returns the latest version reconstructed by sequentially applying the update contents stored in the phase-change memory to the data stored in the flash memory. The method of claim 1,
And not to overwrite the updated data directly with the data stored in the flash memory to update the data stored in the flash memory. The method of claim 1,
And updating the data stored in the flash memory by sequentially applying and applying the update contents to the data stored in the flash memory in the order of occurrence. The method of claim 1,
Data stored in the flash memory is accessed in units of pages, and the update contents are accessed in units of bytes. The method of claim 1,
And said update content is variable in size. The method of claim 1,
And one or more update contents recorded in the upper memory in the phase change memory. The method of claim 1,
The phase change memory allocates update storage space for each block of the flash memory. The method of claim 8,
And wherein the update contents are not fixed in a storage location in the update contents storage space of the phase change memory. The method of claim 8,
The time point at which the data stored in the flash memory is updated is when the update content storage space is full, and the data storage system frees the update content storage space by updating the data stored in the flash memory. The method of claim 1,
Data stored in the flash memory is database data. In the data management method using a data storage system including a flash memory and a phase conversion memory,
(a) loading data into which the update contents stored in the phase change memory are applied to the data stored in the flash memory into the upper memory;
(b) storing updated contents of the data loaded and updated in the upper memory in the phase change memory; And
(c) merging the update contents stored in the phase change memory with data stored in the flash memory to update data stored in the flash memory;
The update content is a difference between the data before updating and the updated data when the data stored in the flash memory is updated in the upper memory,
And updating content storage space of the phase change memory is allocated for each block of the flash memory. 13. The method of claim 12,
The step (b)
And storing one or more update contents recorded in the upper memory at a time in the phase change memory. 13. The method of claim 12,
The step (b)
And storing the update contents in the update contents storage space allocated for each block of the flash memory of the phase change memory. 14. The method of claim 13,
The step (b)
And storing the updated contents sequentially in the order of occurrence in addition to the data previously stored in the updated contents storage space. 14. The method of claim 13,
The step (c)
The data management method performed when there is no available storage space in the update content storage space. 14. The method of claim 13,
The step (c)
The data management method of emptying the update storage space by updating the data stored in the flash memory. 13. The method of claim 12,
And the data stored in the flash memory is database data.

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