Patent Publication Number: US-2023137772-A1

Title: Data storage device and error tolerance selecting method thereof

Description:
FIELD OF THE INVENTION 
     The present invention relates to an access technique for a data storage device, and more particularly to an error tolerance selecting method for the data storage device. 
     BACKGROUND OF THE INVENTION 
     Downgrade Flash all exists numerous bad data columns. When the bad data columns are not detected and removed, it will consume most error correction ability (such as, a number of correctable bits) of the error correction code of the data storage device, even may exceed error correction ability of error correction code, which will result in the storage capacity of the data storage device being reduced when a fireware is installed into the data storage device, and it is easy to cause the reading and writing failure of the data storage device. Wherein the number of bad data columns conflict with the error correction ability of error correction code. That is to say, when the number of bad data columns is more, the correctable correction ability of error correction code is less. Therefore, it is necessary to find out a balanceable selecting method of the error tolerance between the number of bad data columns and the error correction ability of error correction code. 
     SUMMARY OF THE INVENTION 
     The present invention, which provides a data storage device and an error tolerance selecting method thereof, can find a balance between the number of bad data columns and the error correction ability of error correction code, in order to find out the number of bad data columns under the maximum error correction ability of error correction code. 
     The present invention provides an error tolerance selecting method, applied to a data storage device, wherein the data storage device comprises a control unit and a data storage medium, and the data storage medium comprises a plurality of data blocks, each data block comprises a plurality of data columns, and the plurality of data columns are divided into a plurality of chunks. The control unit is configured to execute the error tolerance selecting method at least once, and the selecting method comprises: writing data to the plurality of data blocks; reading written data of the plurality of data blocks as read data; comparing the read data and the write data of each data column in the plurality of data blocks, and calculating a number of error bits in each chunk accordingly; selecting a column with a largest number of error bits in a chunk with a largest number of error bits as a bad data column; calculating a difference value between the number of error bits in the chunk and a first threshold value to store the difference value in an error tolerance list; and selecting a largest difference value in the error tolerance list as an error tolerance and acquiring a number of bad data columns corresponding to the largest difference value; wherein, the first threshold value is a number of correctable error bits of error correction code in the data storage device; wherein, the second threshold value is a total number of recordable bad data columns in the data storage device. 
     The present invention provides a data storage device comprises a data storage medium and a control unit connected to the data storage medium. The data storage medium comprises a plurality of data blocks, wherein each block comprises a plurality of data columns, and the plurality of data columns are divided into a plurality of chunks. The control unit is configured to execute an error tolerance selecting method. The selecting method comprises: writing data to a plurality of data blocks; reading written data of the plurality of data blocks as read data; comparing the read data and the write data of each data column in the plurality of data blocks, and calculating a number of error bits in each chunk; selecting a column with a largest number of error bits in a chunk with a largest number of error bits as a bad data column; calculating a difference value between the number of error bits in the chunk and a first threshold value to store the difference value in an error tolerance list; and selecting a largest difference value in the error tolerance list as an error tolerance and acquiring the number of bad data columns corresponding to the largest difference value; wherein, the first threshold value is a number of correctable error bits of error correction code in the data storage device; wherein, the second threshold value is a total number of recordable bad data columns in the data storage device. 
     In one embodiment of the present invention, each of the plurality of chunks comprises a data area and a spare area. 
     In one embodiment of the present invention, each of the plurality of data blocks comprises a plurality of data pages, each of the plurality of data pages comprises a plurality of data columns which are in the same row. 
     In one embodiment of the present invention, each of the plurality of data pages comprises a data area and a spare area, and the plurality of chunks are in the data area. 
     In one embodiment of the present invention, the first threshold value and the number of the bad data columns are negative correlation. 
     In one embodiment of the present invention, the error tolerance list further stores the number of bad data columns, the number of error bits of the chunk and the first threshold value. 
     The present invention, which provides a data storage device and an error tolerance method thereof, can find a balance between the number of bad data columns and the error correction ability of error correction code, so as to find out the number of bad data columns under the maximum error correction ability of error correction code, and avoid the correctable correction ability of error correction code being greatly reduced in the same time. 
     In order to make the above and other objects, features, and advantages of the present invention more comprehensible, embodiments are described below in detail with reference to the accompanying drawings, as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a data storage device provided by an embodiment of the present invention; 
         FIG.  2    is a schematic diagram of a data storage medium provided by an embodiment of the present invention; and 
         FIG.  3    is a flowchart schematic diagram of an error tolerance selecting method for a data storage device provided by an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in  FIG.  1   ,  FIG.  1    is a schematic diagram of a data storage device provided by an embodiment of the present invention. The data storage device  1  comprises a data storage medium  10  and a control unit  20 , and the control unit  20  is connected to the data storage medium  10 , in order to access data in the data storage medium  10 . 
     As shown in  FIG.  2   ,  FIG.  2    is a schematic diagram of a data storage medium provided by an embodiment of the present invention. The data storage medium  10  comprises a plurality of data blocks (as shown in the labels B 0  to BZ- 1 ). Each data block comprises a plurality of data columns  11 , and the data columns placed in the same row is called a data page (as shown in the labels PO to PZ- 1 ). Further, according to the demand of a user, the data columns  11  are divided into M chunks (as shown in the labels C 0  to CM- 1 ), and each chunk C 0  to CM- 1  comprises a plurality of data columns  11 . Z, N, and M in the above are all positive integers. In this embodiment, the data storage medium  10  is implemented by non-volatile memory, for example, by a memory device with long-term data storage such as Flash memory, Magnetoresistive RAM, Ferroelectric RAM, etc. Moreover, in an embodiment, each data page can be divided into a data area and a spare area, and the M chunks are in the data area. In the other embodiment, each chunk C 0  to CM- 1  can be divided into a data area and a spare area. The data area is configured to store data (or user data), the spare area is configured to store parity codes, and the parity codes are configured to correct error bits of data in the data area. 
     Since the bad data columns exists in the data storage medium  10 , before the data storage medium  10  is divided into the data area and the spare area, the selecting method for error tolerance of the present invention can be configured to effectively determine and record the bad data columns of the data storage medium  10 . After the locations of the bad data columns are determined, then the data area and the spare area are divided. In addition, the divisions of the data area and the spare area are based on a logical division of data management. Therefore, the user can also divide the data area and the spare area in the beginning, and then use the selecting method for the error tolerance of the present invention in order to determine and record the locations of the bad data columns. Finally, the divisions of the data area and the spare area are adjusted. The spirits of the above two data division methods are similar, and the order of execution steps is slightly different, in order to simplify the description of the present invention, only the second embodiment is used for description, but it is not limited thereto. 
     The next thing to explain is, the error tolerance selecting method of the present invention (Hereinafter referred to as the selecting method), may be configured to select the bad data columns in the data storage medium  10 . Moreover, in this embodiment, one of the data blocks B 0  to BZ- 1  in the data storage medium  10  is randomly selected, as a sample block to perform the selecting method, and not all data blocks B 0  to BZ- 1  are used. It should be noted that the skilled in the art can select different number of sample blocks according to the capacity of the data storage medium  10  to perform the selecting method, for example, sixteen sample blocks are selected to perform the selecting method. Therefore, the present invention does not limit the number of sample blocks. In the other embodiment, the present invention can also perform the selecting method for all data blocks B 0  to BZ- 1 . 
     As shown in  FIG.  3   ,  FIG.  3    is a flowchart schematic diagram of an error tolerance selecting method for a data storage device provided by an embodiment of the present invention. The control unit  20  executes the error tolerance selecting method of the present invention including the following steps. In step S 1 , the control unit  20  writes data to a plurality of data blocks. In step S 3 , the control unit  20  reads written data of the plurality of data blocks as read data. In step S 5 , the control unit  20  compares the read data and the write data of each data column in the plurality of data blocks, and calculating a number of error bits in each chunk accordingly. In step S 7 , the control unit  20  selects a column with a largest number of error bits in a chunk with a largest number of error bits as a bad data column. In step S 9 , the control unit  20  calculates a difference value between the number of error bits in the chunk and a first threshold value to store the difference value in an error tolerance list until a number of bad data columns is equal to a second threshold device, wherein the first threshold value is a number of correctable error bits of error correction code in the data storage device, the second threshold value is a total number of recordable bad data columns in the data storage device. In step S 11 , the control unit  20  selects a largest difference value in the error tolerance list as an error tolerance and acquires a number of bad data columns corresponding to the largest difference value. 
     In an embodiment, the data storage medium  10  includes 17,472 data columns  11 , each data column includes 2,560 bits, these data columns are divided into sixteen chunks, each chunk includes 1024 data columns  11 , and the spare area includes 17,472−(16*1,024)=1,088 data column  11 . That is, each chunk can be allocated to sixty eight data columns  11 , so that the error correction code corresponding to the data columns  11  of the spare area provides an ability of 36-bits correction capability for correcting error. The numerical value in this embodiment will change as the capacity of the data storage medium  10 , and the present invention is not limited to the above numerical value. 
     First, the control unit  20  selects a data block (for example, a data block B 0 ) as a sample block and writes data to the sample block, reads written data of the sample block as read data, compares the read data and the written data of each data column  11  in the sample block to calculate the number of error bits of each data column  11  and the number of error bits of each chunk in the sample block accordingly in the same time. For example, the data storage medium  10  includes ten data blocks, each data column  11  of each data block can be allocated 2,560/10=256 bits, and the control unit  20  compares the written data and the read data of each data column  11  including 256 bits to calculate the number of error bits of each data column  11  including 256 bits, and the total number of error bits of each chunk including 1,024 data columns  11 . 
     Then, the control unit  20  selects a chunk with a largest number of error bits (for example, the chunk C 0  in the data block B 0  has a largest number of error bits which is forty seven error bits), and finds out the chunk C 0  has a first data column  11  with a largest number of error bits (for example, one of data columns has eight error bits with the largest number of error bits) and records the first data column  11  as a bad data column in a bad data column table of the data storage device  1 . It should be noted that the total number of the bad data columns recorded in the bad data column table is an upper limit value, which is the second threshold value, which has 1,088 data columns of the spare area in this embodiment, meanwhile the number of correctable error bits of error correction code in the data storage device  1  is the first threshold value, which represents negative correlation with the number of the bad data columns. That is to say, with the number of the bad data columns recorded in the bad data column table increasing, the first threshold value will gradually decrease, as shown in the error tolerance list of Table 1. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 a number of error 
                   
               
               
                 a number of 
                 first 
                 bits in the chunk 
               
               
                 bad data 
                 threshold 
                 with the largest 
               
               
                 columns 
                 value 
                 number of error bits 
                 difference value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 0 
                 36 bits 
                 (chunk C0)47 bits 
                 −11 
               
               
                 1 
                 35 bits 
                 (chunk C0)39 bits 
                 −4 
               
               
                 2 
                 35 bits 
                 (chunk C1)33 bits 
                 2 
               
               
                 3 
                 35 bits 
                 (chunk C1)29 bits 
                 6 
               
               
                 4 
                 34 bits 
                 (chunk C4)28 bits 
                 6 
               
               
                 5 
                 34 bits 
                 (chunk C5)26 bits 
                 8 
               
               
                 6 
                 34 bits 
                 (chunk C10)18 bits 
                 16 
               
               
                 7 
                 32 bits 
                 (chunk C0)17 bits 
                 15 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 200  
                 10 bits 
                 (chunk C5)9 bits 
                 1 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 . 
                 . 
                 . 
                 . 
               
               
                 1088   
                  0 bits 
                 (chunk C6)7 bits 
                 −7 
               
               
                   
               
            
           
         
       
     
     Then, after recording the first data column  11  of chunk C 0  as the bad data column in the bad data column table, the control unit  20  finds out the chunk with a largest number of error bits from all chunk and a second data column  11  with a largest number of error bits in the chunk again (for example, chunk C 0  has the largest number of error bits which is thirty seven error bits, and one of the data columns in the chunk C 0  has a largest number of error bits which is ten error bits) and records the second data column  11  as a bad data column in the bad data column table. Then, after recording the second data column  11  in chunk C 0  as the bad data column in the bad data column table, the control unit  20  finds out the chunk with a largest number of error bits from all chunk and a third data column  11  with a largest number of error bits in the chunk again (for example, chunk Cl has the largest number of error bits which is thirty three error bits, and one of the data columns in the chunk Cl has the largest number of error bits which is four error bits) and records the third data column  11  as a bad data column in the bad data column table. And so on, until the number of 1,088 recordable bad data columns in the data storage device  1  is used up. 
     Finally, the control unit  20  may calculate a difference value between the chunk with the largest number of error bits and the first threshold value to store the difference value in the error tolerance list until the number of the bad data columns is equal to the second threshold value which is 1088 data columns. And the control unit  20  selects the difference value with the largest positive integer as a best error tolerance, such as the value sixteen in the difference value column of the error tolerance list. In other words, an additional 16-bit correction capability can be obtained through the selecting method of the present invention. Meanwhile, the number of bad data columns which is six can be found corresponding, and the available data columns in the spare area is 1,088−6=1,082 data columns. 
     In summary, the present invention, which provides a data storage device and an error tolerance method thereof, can find a balance between the number of the bad data columns and the error correction ability of error correction code, so as to find out the number of bad data columns and the maximum error correction capability of the error correction code, and avoid the error correction ability of the error correction code being greatly reduced. 
     Although the present invention has been disclosed as above with the embodiments, it is not intended to limit the present invention. The ordinary skilled in the art may make some modifications and retouching without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached claims.