The present invention illustrates a method for rebuilding a mapping table, and more particularly, the method for rebuilding a logical to physical mapping table of a solid state disk.
A solid state disk (SSD) can be regarded as a single memory device including several NAND flash memory arrays. Since the number of erasures of a flash memory is limited, data has to be saved in different spaces with dispersive addresses in the NAND flash memory arrays of the SSD. Further, the SSD can use a logical to physical mapping table (hereafter, say “mapping table”) for managing a correlation between logical addresses of the data and physical addresses (i.e., actual addresses of the data saved in a flash memory array) of the data. By using the logical to physical mapping table, data of the SSD can be rapidly searched and accessed.
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In a conventional method for rebuilding the mapping table of the SSD, the SSD usually uses an idle time slot of accessing user data 3 during a time interval for backing up the mapping table to the flash memory array 1 in avoidance of decreasing operation efficiency for accessing user data 3 of the buffer memory 2. When the mapping table starts to back up, the user data 3 is accessed according to a command. If data of the mapping table to be backed up (say, data of the backup mapping table 4) is not much, the SSD can respond to the command generated from a host immediately. Thus, the operation efficiency for accessing the user data 3 can be maintained. However, if data of the backup mapping table 4 is overmuch, it requires a lot of time for writing the backup mapping table 4 to the flash memory array 1. Thus, the SSD may not respond to the command generated from the host. The operation efficiency for accessing the user data 3 may be severely decreased. In an extreme case, the operation efficiency is decreased to zero. In this case, a user may spend a lot of time waiting for the response of the SSD.
In another conventional method for rebuilding the mapping table of the SSD, the backup mapping table 4 and the user data 3 are written to the flash memory array 1 at the same time. Although operation efficiencies for accessing the user data 3 and the backup mapping table 4 are decreased, the operation efficiency for accessing the user data 3 is slightly decreased. In other words, the operation efficiency for accessing the user data 3 can be maintained to a tolerable performance. The extreme case of zero operation efficiency can be avoided here. In other words, spending a lot of time waiting for the response of the SSD by the user can also be avoided.
However, when the backup mapping table 4 is written to the flash memory array 1, user data 5 in front of the user data 3 may also be introduced to the flash memory array 1. The user data 5 may cause some amendments of the backup mapping table 4 saved in the flash memory array 1. When the power is turned off, the user data 3 can be written to the flash memory array 1. Unfortunately, the backup mapping table 4 writing from the buffer memory 2 to the flash memory array 1 cannot be updated according to differences (or say, amendments caused by introducing user data 5). Therefore, when the power is turned on again, the conventional SSD has to read out the backup mapping table 4 in the flash memory array 1. Then, the conventional SSD requires a lot of time to scan all data segments of the memory. Further, the conventional SSD has to search differences for updating and rebuilding the mapping table, leading to decreased operation efficiency or booting efficiency of the SSD. Thus, to develop an efficient method for rebuilding the mapping table of the SSD is still an open question.
The present invention aims at providing a method for rebuilding the mapping table of the solid state disk. When the backup mapping table is written to the flash memory array, differences of the backup mapping table are recorded over time. The backup mapping table and backup differences are saved in the flash memory array. When the power is turned on again, the backup mapping table and the backup differences can be read out. Thus, since the mapping table can be rapidly rebuilt by updating the backup mapping table according to the backup differences, operation efficiency for accessing data can be improved.
The present invention aims at providing a method for rebuilding the mapping table of the solid state disk. When a backup period elapses, record a data page as a flag data page having user data at the same time, record a blank data segment value prepared to be used, and read a recorded flag data page and a data page with recorded data following the recorded flag data page. Further, after the backup period elapses, rebuild entries of a mapping table corresponding to a data page used to save user data according to a sequence of time labels of data pages with recorded data. By doing so, a processing time for rebuilding the mapping table can be reduced.
To achieve aforementioned purposes, a method for rebuilding the mapping table of the solid state disk includes maintaining the mapping table saved on the buffer memory dynamically, backing up the mapping table regularly, processing user data and the backup mapping table simultaneously for writing to the flash memory array, recording differences between the mapping table and the backup mapping table simultaneously during the backup period, backing up the differences to the flash memory array continuously after the backup mapping table is written to the flash memory array, reading the backup mapping table and backup differences after power is turned on, and rebuilding the backup mapping table according to the backup differences in the buffer memory.
Another method for rebuilding the mapping table of the solid state disk includes when the backup period elapses, writing the backup differences to the flash memory array, recording a data page as a flag data page having user data at the same time, and recording a blank data segment value prepared to be used. After the mapping table is generated, read a recorded flag data page, read a data page with recorded data following the recorded flag data page according to a default programming sequence, and read a data page with recorded data from the blank data segment prepared to be used. If time labels of data pages are not increased from a time label of the flag data page, complete a process for rebuilding the mapping table by using a mapping table currently presented. If time labels of the data pages are increased from a time label of the flag data page, update the mapping table currently presented according to the data pages already read, and then complete the process for rebuilding the mapping table.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
For the present invention to achieve above purposes, the use of technology and its effects hereby cite the preferred embodiment, and with the drawings to be described below.
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Additionally, the SSD 15 can perform a garbage collection mechanism regularly. The user data saved in some valid data pages inside a data segment of the flash memory 19 can be read out and then saved in the buffer memory 17. Then, the user data can be saved to another data segment. Then, the data segment is processed by using a data erasure mechanism for generating a blank data segment. The blank data segment can be reserved for saving another user data. In the present invention, the user data processed by the garbage collection mechanism and the user data accessed by using the host 11 can be written to different data segments for improving performance of the SSD 15.
To manage a correlation between a logical address and a physical address of the flash memory array 18, when the SSD 15 is powered up, the SSD 15 can read the managing data from the data segment of each flash memory 19 of the flash memory array 18. Accordingly, the logical address to physical address mapping table 20 (shown in
Since the computational capability of the controller 16 of the SSD 15 is limited by its hardware, the number of processing data during a time interval is also limited. In
When the backup mapping table 22 is saved to the flash memory array 18 during a backup period T, user data 21a may be written to the flash memory array 18. Thus, the mapping table 20 of the buffer memory 17 may be dynamically amended. In other words, the mapping table 20 is different from the backup mapping table 22 since the user data 21a is introduced. The backup mapping table 22 currently transmitted cannot be updated according to the amendments. To ensure correctness of the backup mapping table 22, differences between the “amended” mapping table 20 by accessing the user data 21a and the backup mapping table 22 are also saved in the buffer memory 17. Here, the differences can be a recording log file of the differences (hereafter say, differences 23). Further, after the backup mapping table 22 is completely written to the flash memory array 18, the backup differences 24 are written to the flash memory array 18. When the power is turned off, the buffer memory 17 inherently erases all user data. When the power is turned on again, the SSD 15 can read the backup mapping table 22 and the backup differences 24 from the flash memory array 18 to the buffer memory 17. Then, the SSD 15 can use the backup differences 24 to update the backup mapping table 22 for rebuilding (or say, generating) the mapping table 20 rapidly in the buffer memory 17.
Thus, in the method for rebuilding the mapping table 20 of the SSD 15, when the backup mapping table 22 is written to the flash memory array 18, the differences 23 with respect to accessing another user data are also recorded at the same time. The differences 23 become the backup differences 24 following the backup mapping table 22 and are written to the flash memory array 18. When the power is turned on again, the SSD 15 can use the backup differences 24 to update the backup mapping table 22 for rebuilding the mapping table 20 rapidly. Since the mapping table 20 can be rebuilt rapidly, the operation efficiency of the SSD 15 is satisfactory without introducing additional hardware.
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Since each flash memory 19 has a limited erasure lifetime, when the user data has a big size, the SSD 15 can perform a dispersive data storage process for avoiding erasure lifetime reduction of the flash memory 19. Further, when the backup period T elapses, the backup differences 24 are written to the flash memory array 19. The SSD records the data page 19b with the user data 21b of the data segment 19a of the flash memory 19 as a flag data page 32. Then, the SSD 15 records a blank data segment 33 prepared to be used.
In the flash memory 19, to avoid program voltage interferences between two adjacent data pages 19b, an interval-based voltage programming method can be introduced. Thus, the flash memory 19 includes a default sequence for programming the data pages 19b. When the SSD 15 is powered on, a flag data page 32 is read out. Then, data pages 19b from the blank data segment 33 with recorded data following the recorded flag data page 32 are further read out. When the data pages 19b with time labels increased from the time point t of the time label of the flag data page 32 are found, the mapping table 20 in the buffer memory 17 can be updated according to the data pages 19b. By doing so, the mapping table 20 can be rebuilt or updated without scanning all data segments of the SSD 15.
To sum up, a method for rebuilding the mapping table of the SSD is disclosed. When a backup period elapses, a data page can be recorded as a flag data page having user data at the same time. Blank data segments following the flag data page are also recorded. When the power is turned on again, the SSD can read the flag data page and data pages with recoded data from the blank data segments following the flag data page. Based on a time point labeled on the flag data page, the data pages with recent time labels can be found. Then, the mapping table can be updated accordingly. Thus, a processing time for rebuilding or updating the mapping table can be reduced.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Number | Date | Country | Kind |
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201611037058.9 | Nov 2016 | CN | national |