Abstract:
An apparatus includes an interface, and a processor. The interface inputs and outputs data from and to a storage device that includes a plurality of memory blocks forming a plurality of RAID groups, and a backup block used as a backup of the plurality of memory blocks. The processor sets as read-out targets a plurality of memory cells included in each memory block. When a memory cell included in a faulty memory block becomes a read-out target, the processor excludes the memory cell that belongs to the RAID group, until restoration of the data of the faulty memory block and copying of the restored data to the backup block are completed. When the copying of the restored data is completed, the processor selects as read-out targets the memory cell that belongs to the RAID group that includes the faulty memory block and a memory cell in the backup block.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2013-261803, filed on Dec. 18, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a method for reading out data from a memory. 
     BACKGROUND 
     A server device is mounted with an SSD (Solid-State Drive) and an HDD (Hard Disk Drive) as a storage device. The HDD is a storage device that rotates at high speed a disk-shaped disk coated with a magnetic substance and moves a magnetic head, and thus reads out information stored in the disk. The SSD is a storage device that uses a NAND-type flash memory as a storage medium. The server device has a patrol-read function that performs a normality diagnosis of a medium by reading each memory such as the SSD and the HDD. 
     The SSD has a plurality of memory blocks (blocks). Each memory block has a plurality of pages. In addition, each page has a plurality of memory cells. A control unit that controls processing of the normality diagnosis diagnoses normality in units of memory cells. The control unit specifies the head address of a memory cell that is a diagnosis target. The SSD reads out data from the memory cell that includes the specified address, and sends back the data to the control unit. When the control unit receives the data of the memory cell that includes the specified address from the SSD, the control unit determines that the memory cell is normal. The control unit sequentially specifies the head addresses of memory cells on which the normality diagnosis has not yet been performed, and the normality diagnosis is also performed on the remaining memory cells. When the SSD cannot read data from the memory cell that includes the specified address, the SSD notifies the control unit that the memory cell is faulty. 
     In the storage device that uses a NAND-type flash memory such as the SSD, a failure in units of blocks occurs due to aging deterioration, etc. A failure due to deterioration is anticipated in advance. Therefore, the medium such as the SSD has a backup block. The control unit regards a block in which a failure has occurred as a faulty block, and replaces the faulty block with the backup block. The SSD maintains the initial capacity of the medium by replacing the capacity of the faulty block with that of the backup block. 
     In order to replace the faulty block with the backup block, the control unit recovers data stored in the faulty block, and then arranges the recovered data in the backup block. Examples of methods for recovering data include an ECC (Error-Correcting Code) and a RAID (Redundant Array of Inexpensive Discs). Such a restorable error is referred to as a retryable error. 
     A technique for setting NAND memory blocks as one group, and creating parity data and writing it as nth data every time n-1th data is written is known as a technique for data restoration in the SSD. (See, for example, Patent document 1) 
     A technique for diagnosing the address that is an access target and executing sequential read on the basis of a request from outside is known as a technique related to patrol read. (See, for example, Patent document 2) 
     Patent Document 1: Japanese Laid-open Patent Publication No. 2010-152551 
     Patent Document 2: Japanese Laid-open Patent Publication No. 2012-247817 
     SUMMARY 
     According to an aspect of the embodiments, a storage control apparatus includes an interface and a processor. The interface inputs and outputs data to and from a storage device that includes a plurality of memory blocks that create a plurality of RAID groups, and that further includes a backup block used as a backup of the plurality of memory blocks. When the processor sets a plurality of memory cells included in each memory block in the storage device as read-out targets, the processor sometimes selects a memory cell included in a faulty memory block as a read-out target. Then, the processor excludes the memory cell that belongs to the RAID group having the faulty memory block from the read-out targets until restoration of data of the faulty memory block and copying of restored data in the backup block are completed. At the same time, the processor selects a memory cell of a group other than the RAID group having the faulty memory group as a read-out target. When the restoration of the data of the faulty memory block and copying of the restored data in the backup block is completed, the processor selects the memory cell that belongs to the RAID group having the faulty memory block and a memory cell in the backup block as read-outs targets. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram explaining an example of normality diagnosis processing related to embodiment 1. 
         FIG. 2  is a diagram illustrating one example of a storage system in the embodiments. 
         FIG. 3  is a sequence diagram explaining an example of normality diagnosis processing related to embodiment 1. 
         FIG. 4A  is a sequence diagram explaining an example of normality diagnosis processing related to embodiment 2. 
         FIG. 4B  is a sequence diagram explaining an example of normality diagnosis processing related to embodiment 2. 
         FIG. 5  is a sequence diagram explaining an example of processing for resuming an interrupted normality diagnosis. 
         FIG. 6A  is a diagram explaining examples of information tables used for the normality diagnosis. 
         FIG. 6B  is a diagram explaining examples of information tables used for the normality diagnosis. 
         FIG. 7  is a diagram explaining processing for performing the normality diagnosis on a head block for each group. 
         FIG. 8  is a diagram explaining an example of a storage apparatus that includes an SSD and an HDD. 
         FIG. 9A  is a flowchart explaining an example of normality diagnosis processing used for the SSD. 
         FIG. 9B  is a flowchart explaining an example of normality diagnosis processing used for the SSD. 
         FIG. 10A  is a flowchart explaining normality diagnosis processing that is performed until the arrangement of restored data in a backup block is completed. 
         FIG. 10B  is a flowchart explaining normality diagnosis processing that is performed until the arrangement of the restored data in the backup block is completed. 
         FIG. 11  is a flowchart explaining an example of processing for performing the normality diagnosis on a group for which the normality diagnosis is skipped. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As one example, a case in which a block that has three memory cells, i.e., a memory cell A, a memory cell B, and a memory cell C, is faulty is considered. The failure of the block is a retryable error. When a control unit performs a normality diagnosis and specifies the head address of the memory A, an SSD cannot read data stored in the memory cell A and detects the failure. The SSD notifies the control unit that the block is faulty. The SSD executes processing for recovering data of the faulty block and arranging the recovered data in a backup block. On the other hand, the control unit starts the normality diagnosis of the next memory cell B without interrupting normality diagnosis processing. When the data recovery of the faulty block and the arrangement of the recovered data in the backup block are not completed, the SSD cannot read the data stored in the memory cell B, detects that the block is faulty, and notifies the control unit of it. Thereafter, the control unit continues performing the normality diagnosis on the memory C. Then, the SSD cannot read the data stored in the memory cell C, detects that the block is faulty, and notifies the control unit of it. 
     When the normality diagnosis is performed on a faulty block, the control unit is notified of a plurality of errors until the data recovery of the faulty block and the arrangement of the recovered data in the backup block are completed, after a first memory cell is diagnosed. When a predetermined number of errors are detected, the control unit determines that the SSD is a troubled storage device, and will not use the SSD thereafter. However, even when one block is faulty, if the failure is a retryable error, data is restored and a backup area is used as a replacement, so there is no influence on the function of the SSD after the data is restored. As described above, there are cases in which the control unit determines that the SSD is a troubled storage device, as a function of the SSD, even if the failure is a retryable error that is supposed to be acceptable. In one aspect, the object of the embodiments is to efficiently perform the normality diagnosis. 
     Hereinafter, the embodiments will be described in detail with reference to the drawings. 
       FIG. 1  is a diagram explaining an example of the normality diagnosis processing related to embodiment 1. A storage apparatus  100  in  FIG. 1  includes a control unit  101  and an SSD  110 . The control unit  101  controls the normality diagnosis processing on the SSD. The SSD  110  is a storage device that uses an NAND flash memory  117  as a storage medium, and includes a plurality of blocks  111  ( 111   a  to  111   f ) and a backup block  111   g.  The block  111  includes a plurality of memory cells that are memory management units. The SSD  110  includes a management unit  115 . The management unit  115  manages data stored in each block in the SSD  110 . 
     As one example, the block  111   a,  the block  111   b,  and the block  111   c  of the SSD  110  in  FIG. 1  are one group. The group can hold data, for example, by using a RAID 5. Therefore, when there is original data AA, the management unit  115  divides the data AA into two pieces of data, i.e., A1 and A2, and creates parity for the data AA. The management unit  115  stores parity data for the data A1, A2, and AA in the block  111   a,  the block  11   b,  and the block  111   c,  respectively. Similarly, the management unit  115  divides data BB into two pieces of data, i.e., B1 and B2, and creates parity for the data BB. The management unit  115  stores parity data for the data B1, B2, and BB in the block  111   a,  the block  111   b,  and the block  111   c , respectively. The data AA and the data BB are different data. 
     Data such as A1, B1, and the parity are held in a memory cell in each block. The memory cell  201   a  in the block  111   a  holds the data A1, and the memory cell  201   b  holds the data B1. The memory cell  202   a  of the block  111   b  holds the data A2, and the memory cell  202   b  holds the data B2. The memory cell  203   a  of the block  111   c  holds the parity for the data AA, and the memory cell  203   b  holds the parity for BB. The block  111   d,  the block  111   e,  and the block  111   f  are one group. The blocks  111   d  to  111   f  hold M1 and M2 obtained by dividing MM, and parity for the data MM. The blocks  111   d  to  111   f  hold N1 and N2 obtained by dividing NN, and parity for the data NN. As a result, the group of the blocks  111   a  to  111   c,  and the group of the blocks  111   d  to  111   f  store different data. 
     Hereinafter, an example of the normality diagnosis processing related to embodiment 1 when the block  111   b  is faulty will be described in order. The normality diagnosis executes processing in order in units of memory cells. 
     (A1) The control unit  101  starts the normality diagnosis of the SSD  110 . 
     (A2) The control unit  101  specifies the head address of the memory cell  201   a  of the block  111   a,  and notifies the management unit  115  of the read-out request of the data held by the memory cell that includes the specified address. 
     (A3) The management unit  115  reads out the data in the memory cell  201   a  in a cache area  116 . In addition, in order to maintain the consistency of the RAID, the management unit  115  reads out the data A2 divided from AA that is the original data of A1 and the parity data in the cache area  116  of the SSD  110 . 
     However, since the block  111   b  is faulty, the SSD  110  cannot read out the data A2 from the block  111   b.    
     (A4) The management unit  115  detects that the data cannot be read out from the block  111   b.    
     (A5) The management unit  115  determines whether or not the detected failure is a retryable error. The determination on whether or not the detected failure is a retryable error is made on the basis of whether or not the data stored in the block  111  that includes the data A2 can be restored using the parity of an ECC or the RAID. The management unit  115  notifies the control unit  101  of the occurrence of the retryable error.
 
(A6) When the detected error is a retryable error, the management unit  115  restores the data of the block  111   b,  and arranges the data in the backup block  111   g.  The data arranged in the backup block  111   g  is stored while the same address as that of the block  111   b  is specified therefor.
 
(A7) The control unit  101  skips the normality diagnosis of the group that includes the faulty block  111   b.  The control unit  101  continues the normality diagnosis with respect to the group that does not include the faulty block  111   b.  For example, the control unit  101  sequentially specifies the head addresses of the memory cells in order of, for example, the memory cell  204   a  and the memory cell  204   b  of the block  111   d , and gives a notification of the read-out request of the data held by the memory cell that includes the specified address. The management unit  115  transmits to the control unit  101  the data of the memory cell that includes the specified address. The control unit  101  determines that the memory cell that includes the specified address is normal.
 
(A8) The control unit  101  determines whether or not the normality diagnosis of all the blocks other than the group subjected to skip processing is completed. When the control unit  101  determines that the normality diagnosis of all the blocks other than the group subjected to skip processing is completed and the arrangement of the data in the backup block  111   g  is completed, the control unit performs the normality diagnosis on the group (the blocks  111   a  to  111   c ) subjected to skip processing. When the management unit  115  reads out the data held by the block  111   b,  the management unit reads out the data from the backup block  111   g  as an alternative.
 
(A9) When the normality diagnosis of all the blocks  111  is completed, the control unit  101  terminates the normality diagnosis processing.
 
     When, as a result of (A5), the detected failure is not the retryable error, the control unit  101  does not perform processing in (A6) and (A8). When the control unit  101  detects a faulty block in the normality diagnosis in (A7), the control unit repeats the processing from (A5). The SSD in  FIG. 1  does not limit the number of the blocks and the number of the memory cells. The data such as A1 to A2 is one example, and does not limit the data in any way. Although three blocks such as the block  111   a,  the block  111   b,  and the block  111   c  are set as one group in embodiment 1, a greater plurality of blocks may be set as one group. 
     Since the normality diagnosis processing for a group that includes a block in which a failure is detected is skipped, an error is detected in the normality diagnosis for a group that includes a faulty block once. As a result, even when a faulty block is diagnosed, since normality diagnosis is not performed a plurality of times on the faulty block, error detection is not performed a plurality of times on one block. 
       FIG. 2  illustrates one example of a storage system in the embodiments. The storage system  11  is a disk storage system mounted with a plurality of disk devices  19 . With respect to an access from a host computer (hereinafter referred to as a host)  21  to the disk device  19 , two access paths exist for each disk device  19  for redundancy. As for data itself, data is dispersed in a plurality of disks using the RAID, and is stored in a redundant state. 
     The storage system  11  includes the host computer (hereinafter referred to as the host)  21 , a fiber channel (FC) switch  22 , a controller enclosure (CE)  12 , and a drive enclosure (DE)  18 . In the storage system  11 , the drive enclosure (DE)  18  and the host  21  are connected to each other via the FC switch  22  and controller modules (CM)  13 . 
     The host  21  communicates with the controller enclosure (CE)  12  via the FC switch  22 , and reads out data from the disk device  19  included in the drive enclosure (DE)  18  or writes data in the disk device  19 . In  FIG. 2 , the one host  21  is illustrated; however, a plurality of hosts  21  may be connected to the controller enclosure (CE)  12 . 
     The controller enclosure (CE)  12  includes the plurality of controller modules (CMs)  13 . The controller module  13  controls operation of the disk device  19 . Each controller module  13  functions as a storage control apparatus. Since the storage system  11  includes two or more controller modules (CMs)  13  used for operation, redundancy is secured. 
     The controller module (CD)  13  transmits to the drive enclosure (DE)  18  an input/output (I/O) command as access instruction information, and gives an input/output command of data with respect to the storage area of the disk device  19 . When the controller module (CM)  13  cannot receive a response after an access monitoring time has passed from the input/output command, the controller module transmits to the drive enclosure (DE)  18  an abort instruction command that interrupts I/O processing. 
     The controller module  13  includes a channel adapter (CA)  14 , a central processing unit (CPU)  15 , a storage unit  16 , and a device adapter (DA)  17 . The channel adapter (CA)  14 , the CPU  15 , the storage unit  16 , and the device adapter (DA)  17  are connected to one another via an internal bus. The CPU  15  operates as the control unit  101 . 
     The channel adapter (CA)  14  is connected to the host  21  via the FC switch  22 . The CPU  15  controls the whole of the controller module  13 . 
     The storage unit  16  is a device that records information on for example a cache memory, a ROM (Read Only Memory), or a RAM (Random Access Memory). The storage unit  16  stores data used for operating the controller module  13 , a program related to the embodiments, and data etc. used for the embodiments. 
     The device adapter (DA)  17  is connected to the drive enclosure (DE)  18 . The CPU  15  transmits and receives data between the drive enclosure (DE)  18  and itself via the device adapter  17 . 
     The drive enclosure (DE)  18  is formed of one or more drive enclosures (DEs). The drive enclosure (DE)  18  includes the plurality of disk devices  19 , and has a RAID configuration that takes redundancy into consideration. The disk device  19  is not limited to a hard disk drive (HDD), and for example, an SSD (Solid State Drive) or a magneto-optical disk is possible. In the embodiments, the disk device  19  is used as one example of the storage device, but the embodiments are not limited to this, and a storage device is possible for which either an access method of a random access or a sequential access is possible. 
       FIG. 3  is a sequence diagram explaining an example of the normality diagnosis processing related to embodiment  1 . The same storage apparatus as that in  FIG. 1  is used for the description of the sequence diagram in  FIG. 3 . The control unit  101  specifies the head address of the memory cell  201   a  of the block  111   a,  and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 101 ). The management unit  115  reads out the data in the memory cell  201   a  in the cache area  116 . In addition, the management unit  115  tries to read out A2 divided from the AA that is the original data of A1 in the cache area  116  in order to maintain the consistency of the RAID; however, the management unit cannot read out the A2 data from the block  11   b,  because the block  111   b  is faulty. The management unit  115  notifies the control unit  101  that a retryable error has occurred (step S 102 ). The management unit  115  restores the data of the faulty block (step S 103 ). The management unit  115  arranges the restored data in the backup block  11   g  (step S 104 ). The control unit  101  counts the occurrences of the retryable error (step S 105 ). Here, S 103  to S 104  and S 105  are performed in parallel. 
     The control unit  101  skips the normality diagnosis of the group that includes the faulty block  111   b,  and sets a memory cell of the group other than the skipped group as a target for the normality diagnosis. In order to continue the normality diagnosis, the control unit  101  specifies the head address of the memory cell  204   a  of the block  111   d,  and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 106 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 107 ). The control unit  101  specifies the head address of the memory cell  204   b  of the block  111   d,  and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 108 ). The management unit  115  reads out data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 109 ). 
     The restoration of data and the arrangement of the restored data in the backup block  111   g,  which are processing in S 104 , are completed (step S 110 ). The control unit  101  completes the normality diagnosis of all the blocks of the group other than the group subjected to skip processing (step S 111 ). Here, S 110  and S 111  may be in reverse order. The next S 112  processing is executed after completion of S 110  and S 111 . 
     The control unit  101  performs the normality diagnosis on the group subjected to skip processing. The control unit  101  specifies the head address of the memory cell  201   a  of the block  111   a,  and notifies the management unit  115  of the request to read out the data held by the memory cell that includes the specified address (step S 112 ). The management unit  115  reads out the data from the memory cell that includes the specified address and transmits it to the control unit  101  (step S 113 ). The control unit  101  repeats steps S 112  and S 113 , and when the normality diagnosis of all the blocks  111  is completed, the normality diagnosis processing is terminated. 
     Modification Example of Normality Diagnosis 
     In normality diagnosis processing related to embodiment 2, after restored data is arranged in the backup block due to a retryable error, continuing normality confirmation processing is interrupted, and the normality diagnosis of the group for which the normality diagnosis was skipped is performed. 
     Hereinafter, an example of the normality diagnosis processing related to embodiment 2 when the block  111   b  is faulty will be described in order. The normality diagnosis related to embodiment 2 is processing that is executed after the processing (A1) to (A6) of the normality diagnosis related to embodiment 1. The same storage apparatus as that in FIG.  1  is used for the description of the normality diagnosis processing related to embodiment 2. 
     (B1) The control unit  101  skips the normality diagnosis of the group that includes the faulty block  111   b.  The control unit  101  continues the normality diagnosis from the block  111   d  of the group that does not include the faulty block  111   b.  For example, the control unit  101  sequentially specifies the head addresses of the memory cells in order of the memory cell  204   a , the memory cell  204   b,  etc., and gives the notification of a request to read out the data held by the memory cell that includes the specified address. The management unit  115  transmits to the control unit  101  the data of the memory cell that includes the specified address. The control unit  101  determines that the memory cell that includes the specified address is normal. In addition, the control unit  101 , every time it receives data from the management unit  115 , notifies the management unit  115  of a request to confirm whether or not the arrangement of the restored data in the backup block  111   g  is completed.
 
(B2) When the arrangement of the restored data in the backup block  111   g  is completed, the control unit  101  interrupts the normality diagnosis processing currently being executed, and performs the normality diagnosis on the group for which the normality diagnosis processing was skipped.
 
(B3) The normality diagnosis targeted at the group for which the normality diagnosis was skipped is completed. The control unit  101  resumes the interrupted normality diagnosis.
 
(B4) The control unit  101  determines whether or not the normality diagnosis of all the blocks  111  is completed. When the normality diagnosis of all the blocks  111  is completed, the control unit  101  terminates the normality diagnosis processing.
 
       FIGS. 4A and 4B  are each a sequence diagram explaining an example of the normality diagnosis processing related to embodiment 2. The same storage apparatus as that in  FIG. 1  is used for the description of the sequence diagrams in  FIGS. 4A and 4B .  FIG. 4A  is an example of the case in which the normality processing is initiated with respect to the SSD. The control unit  101  specifies the head address of the memory cell  201   a  of the block  111   a,  and notifies the management unit  115  of the request to read out the data held by the memory cell that includes the specified address (step S 201 ). The management unit  115  reads out the data in the memory cell  201   a  in the cache area  116 . In addition, the management unit  115  tries to read out A2 divided from AA, which is the original data of A1, in the cache area  116  in order to maintain the consistency of the RAID; however, since the block  111   b  is faulty, the management unit cannot read out the A2 data from the block  111   b.  The management unit  115  notifies the control unit  101  that a retryable error has occurred (step S 202 ). The management unit  115  restores the data of the faulty block (S 203 ). The management unit  115  arranges the restored data in the backup block  111   g  (step S 204 ). The control unit  101  counts the occurrence of the retryable error (step S 205 ). Here, S 203  to S 204  and S 205  are executed in parallel. 
     The control unit  101  skips the normality diagnosis of the group that includes the faulty block. The control unit  101  sets the head address of the memory cell  204   a  of the block  111   d  as the focused-on address that is the address of the memory cell that is the next target for the normality diagnosis. In addition, the control unit  101  transmits to the management unit  115  the request to confirm whether or not the arrangement of the data in the backup block  111   g  in S 204  is completed (step S 206 ). The management unit  115  notifies the control unit  101  that the arrangement of the data in the backup block  111   g  is not completed, as a response to the confirmation request from the control unit  101  (step S 207 ). The control unit  101  adds 1 to the count of wait_patrol (step S 208 ). 
     The control unit  101  skips the normality diagnosis of the group that includes the faulty block  111   b,  and performs the normality diagnosis on the memory cells of the group other than the group for which the normality diagnosis was skipped. In order to continue the normality diagnosis, the control unit  101  specifies the head address of the memory cell  204   a  of the block  111   d,  and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 209 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 210 ). The control unit  101  transmits to the management unit  115  the request to confirm whether or not the arrangement of the data in the backup block  111   g  in S 204  is completed (step S 211 ). The management unit  115  notifies the control unit  101  that the arrangement of the data in the backup block  111   g  is not completed, as a response to the confirmation request from the control unit  101  (step S 212 ). The control unit  101  adds 1 to the count of wait_patrol (step S 213 ). The control unit  101  specifies the head address of the memory cell  204   b  of the block  111   d,  and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 214 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 215 ). The control unit  101  transmits to the management unit  115  the request to confirm whether or not the arrangement of the data in the backup block  111   g  in S 204  is completed (step S 216 ). As a response to the confirmation request from the control unit  101  (step S 217 ), the management unit  115  notifies the control unit  101  that the arrangement of the data in the backup block  111   g  is not completed. The control unit  101  adds 1 to the count of wait_patrol (step S 218 ). 
     After S 218 , the control unit  101  and the management unit  115  continue the normality diagnosis as in S 209  to S 210  and S 214  to S 215  until the processing for arranging the data in the backup block  111   g  in S 204  is completed. In addition, every time the data of the memory cell that includes the specified address is received from the management unit  115 , the control unit  101  and the management unit  115  communicate with each other in order to confirm whether or not the arrangement of the data in the backup block  111   g  has been completed in the same manner as in S 211  to S 213  and S 216  to S 218 . 
       FIG. 4B  is a sequence diagram explaining an example of normality diagnosis processing after completion of data arrangement in the backup block. The control unit  101  specifies the head address of a memory cell XX, and notifies the control unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 301 ). The memory cell XX is a memory cell that is subjected to the normality diagnosis that continues after S 218 , when the arrangement of the data in the backup block  111   g  is completed. The control unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 302 ). The control unit  101  transmits the request to confirm whether the arrangement of the data in the backup block  111   g  in S 204  is completed (step S 303 ). As a response to the confirmation request from the control unit  101 , the management unit  115  notifies the control unit  101  that the arrangement of the data in the backup block  111   g  is completed (step S 304 ). The control unit  101  adds 1 to the count of wait_patrol (step S 305 ). 
     The control unit  101  interrupts the normality diagnosis that has been being performed since S 209 . The control unit  101  performs the normality diagnosis on the group subjected to skip processing. The control unit  101  specifies the head address of the memory cell  201   a  of the block  111   a , and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 306 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 307 ). 
     The control unit  101  specifies the head address of the memory cell  201   b  of the block  111   a,  and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 308 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 309 ). 
     After S 309 , the control unit  101  and the management unit  115  continue the normality diagnosis in the same manner as in S 306  to S 308  until the normality diagnosis reaches the address set as the focused-on address. 
       FIG. 5  is a sequence diagram explaining an example of processing for resuming the interrupted normality diagnosis. The sequence diagram in  FIG. 5  illustrates processing that is executed after all the normality diagnoses of the group for which the normality diagnosis was skipped are completed. The same storage apparatus as that in  FIG. 1  is used for the description of the sequence diagram in  FIG. 5 . The control unit  101  specifies the head address of the last memory cell of the group for which the normality diagnosis was skipped, and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 401 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 402 ). The control unit  101  sets as the next diagnosis target the memory cell after the memory cells of the count number of wait_patrol from the last memory cell of the group for which the normality diagnosis was skipped (step S 403 ). The control unit  101  clears the count value of wait_patrol (step S 404 ). Here, the memory cell after the memory cells of the count number of wait_patrol from the last memory cell of the group for which the normality diagnosis was skipped is the next memory cell of the memory cell XX. 
     The control unit  101  specifies the head address of the next memory cell of the memory cell XX, and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 405 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step S 406 ). The control unit  101  specifies the head address of the memory cell after two memory cells from the memory cell XX, and notifies the management unit  115  of a request to read out the data held by the memory cell that includes the specified address (step S 407 ). The management unit  115  reads out the data from the memory cell that includes the specified address, and transmits the data to the control unit  101  (step  408 ). If the normality diagnosis of all the blocks  111  is completed, the control unit  101  terminates the normality diagnosis processing. 
       FIGS. 6A and 6B  are each a diagram explaining an example of an information table used for the normality diagnosis.  FIG. 6A  is the information table used when a retryable error occurs. The information table used when a retryable error occurs holds the information of the head address of a memory cell in which a retryable error is detected, and the address of the information table used when another retryable error occurs, while associating them with each other. 
     When the control unit  101  receives the notification of a first retryable error, the control unit creates an error table (ERR_TBL)  301   a.  The error table  301   a  holds the head address of the memory cell in which the retryable error is detected. In the case in which the control unit  101  receives the notification of the second retryable error, the control unit creates an error table  301   b.  The case of detecting the second retryable error is when a failure occurs in a block different from the block in which the first retryable error occurs. The control unit  101  causes the error table  301   a  to store the address information of the error table  301   b,  and further causes the error table  301   b  to hold the head address of the memory cell in which the second retryable error is detected. In the case in which the control unit  101  receives the notification of the retryable error of the third time, the control unit creates an error table  301   c.  The case of detecting the retryable error of the third time is when a failure occurs in a block different from the blocks in which the first and second retryable errors occur. The control unit  101  causes the error table  301   b  to store the address information of the error table  301   c,  and further causes the error table  301   c  to hold the head address of the memory cell in which the retryable error of the third time is detected. When a greater plurality of the retryable errors are detected, the control unit  101  creates error tables  301  for the number of the retryable errors. When the normality diagnosis of the block that includes the memory cell corresponding to the address held in the error table  301  is completed, the control unit  101  deletes the error table  301 . 
       FIG. 6B  illustrates information tables used for confirming whether or not the arrangement of data in the backup block is completed. The information table used for confirming whether or not the arrangement of the data in the backup block is completed holds a focused-on address and the number of confirmation requests while associating them with each other. In addition, the information table used for confirming whether or not the arrangement of the data in the backup block has been completed holds the address information of another information table used for confirming whether or not the arrangement of data in the backup block has been completed. 
     The control unit  101  creates a wait_seqrd table  302   a  when requesting confirmation for the first time after the first retryable error. The wait_seqrd table  302   a  holds the head address of the memory cell for which the address is set as the focused-on address in S 206 . The control unit  101  adds the number of times confirmation requests are made for each confirmation request after the first retryable error, and causes the wait_seqrd table  302   a  to hold the number of times confirmation requests are made. 
     Next, the control unit  101  creates a wait_seqrd table  302   b  when requesting confirmation for the first time with respect to data movement to the backup block based on the second retryable error. The control unit  101  causes the wait_seqrd table  302   a  to store the address information of the wait_seqrd table  302   b.  The wait_seqrd table  302   b  holds the head address of the focused-on address set by the second retryable error. In addition, the control unit  101  causes the wait_seqrd table  302   b  to hold the number of times the confirmation requests are made for each confirmation request with respect to the data movement to the backup block based on the second retryable error. 
     Next, the control unit  101  creates a wait_seqrd table  302   c  when requesting confirmation for the first time with respect to the data movement to the backup block based on the retryable error of the third time. The control unit  101  causes the wait_seqrd table  302   b  to store the address information of the wait_seqrd table  302   c.  The wait_seqrd table  302   c  holds the head address of the focused-on address set by the retryable error of the third time. In addition, the control unit  101  adds the number of times the confirmation requests are made for each confirmation request with respect to the data movement to the backup block based on the retryable error of the third time, and causes the wait_seqrd table  302   c  to hold the number of times the confirmation requests are made. When the retryable errors are detected a greater plurality of times, the control unit  101  creates wait_seqrd tables  302  for the number of the retryable errors. When the wait_seqrd table  302  is used due to a resuming of a patrol read in the same manner as in S 405 , the control unit  101  deletes the table that was used. 
     Example of Normality Diagnosis Processing used for SSD 
       FIG. 7  is a diagram explaining an example of processing for performing the normality diagnosis on the head block for each group. In the normality diagnosis processing illustrated in  FIG. 7 , the head block is diagnosed for each group that includes the plurality of blocks, and the diagnosis on the remaining blocks is not performed. When a retryable error is detected, the normality diagnosis processing illustrated in  FIG. 7  introduces the examples of the normality diagnosis described in embodiment 1 and embodiment 2. 
     The SSD  110  in  FIG. 7  includes the plurality of blocks  111  and the cache area  116 . The SSD  110  includes the group of the RAID 5 (31+1) that includes the blocks 111 a1  to 111 a32 . Similarly, the blocks 111 bb1  to 111 b32  and the blocks 111 c1  to 111 c32  are the groups of the RAID 5 (31+1). In the RAID 5 (31+1), one piece of data is divided into 31 equal pieces, and for example, they are held in the blocks 111 a1  to 111 a31 . In the SSD  110  in  FIG. 7 , one piece of data is divided and held in the memory cells 0 to 31. Each group of the RAID 5 (31+1) holds parity. 
     When the normality diagnosis is performed on a storage medium such as the SSD  110  that has a plurality of groups of the RAID 5 (31+1), the control unit  101  may diagnose at least one block for each RAID group. As one example, when the data in the memory cell 0 of the block 111 a1  is read out, the management unit  115  reads out data divided from the original data of the data stored in the memory cell 0 in order to confirm the consistency of the RAID. The management unit  115  reads out the data of the memory cells 1 to 31 and the parity in the cache area  116  of the SSD  110 . 
     When the normality diagnosis on the block 111 a1  is terminated, and next, the normality analysis is performed on the block 111 b1 , the control unit  101  diagnoses the memory cell 1. In the case in which the control unit  101  specifies the head address of the memory cell 1, the data of the memory cell 1 is already read out in the cache area  116 . As a result, even if the management unit  115  receives a request to read out the data of the memory cell 1, the management unit does not read out the data from the memory cell 1, and reads out the data from the cache area  116  instead. Thereafter, when the control unit  101  specifies the address of each of the memory cells 2 to 31, the management unit  115  reads out each piece of data from the cache area  116 . Therefore, the read-out request from the control unit  101  that specifies the memory cells 1 to 31 and the parity does not perform the normality diagnosis on the block that is a storage medium. 
     When the management unit  115  receives the read-out request of the memory cell 0 from the control unit  101 , the management unit reads out the memory cell 0 in the cache area  116 , and reads out the data of the memory cells 1 to 31 and the parity in the cache area  116 . Therefore, the control unit  101  gives the read-out request to one memory cell, which results in the normality diagnosis being performed on the block  111  that holds the data of the memory cells 0 to 31 and the parity. As a result, when a normality diagnosis is performed on a storage medium that has a plurality of RAID 5 groups, the control unit  101  may diagnose at least one block for each RAID 5 group. 
     Embodiment 1, embodiment 2, and the example of the processing for diagnosing at least one block for each group are not limited to the normality diagnosis. Embodiment 1, embodiment 2, and the example of the processing for diagnosing at least one block for each group can be applied to processing that accompanies reading operations in all the pages and the blocks in the SSD for each memory cell. The examples of such processing include rebuild processing and copy back. In the rebuild processing, a reading operation for each memory cell is performed when reading out data from a mirror of a faulty SSD in RAID 1, RAID 1+0, etc. In the copy back processing, a reading operation for each memory cell is performed when copying data from another storage medium in the case in which a faulty SSD in a RAID is replaced. 
       FIG. 8  is a diagram explaining an example of the storage apparatus that includes the SSDs and the HDDs. The storage apparatus  100  includes a control unit  101   a  and a control unit  101   b,  the SSDs  110  ( 110   a  to  110   d ), and the HDDs  220  ( 220   a  to  220   h ). 
     The control unit  101   a  controls processing targeted at the HDDs  220   a  to  220   d,  and the SSDs  110   a  to  110   b.  The control unit  101   b  controls processing targeted at the HDDs  220   e  to  220   h,  and the SSDs  110   c  to  110   d.  The control unit  101  is, for example, a RAID controller. The control unit  101  controls processing such as the normality diagnosis, rebuild, and copy back by way of communication with an outside device. When the control unit  101  performs processing such as the normality diagnosis, the rebuild, and the copy back, the control unit determines whether the processing target is the HDD  220  or the SSD  110 . Whether the processing target is the HDD  220  or the SSD  110  is determined by specifying the type of the medium by using a SCSI command, for example. When the processing target is the HDD  220 , the control unit  101  executes processing such as the normality diagnosis, the rebuild, and the copy back. When the processing target is the SSD  110 , the control unit  101  executes processing for reading the head block for each memory cell, with respect to each group that includes the plurality of blocks. When the processing target is the SSD  110  and a failure is detected therein, the control unit  101  executes processing in embodiments 1 and 2. 
       FIGS. 9A and 9B  are each a flowchart explaining an example of the normality diagnosis processing used for the SSD. The same storage apparatus as that in  FIG. 1  is used for description of the flowcharts in  FIGS. 9A and 9B . The control unit  101  executes the normality diagnosis for each memory cell, targeted at the head block for each group (step S 501 ). The control unit  101  determines whether or not the response of the normality diagnosis from the management unit  115  is a notification of a retryable error (step S 502 ). The control unit  101  skips the normality diagnosis of the group that includes a faulty block, and continues the normality diagnosis of the group that does not include the faulty block until the arrangement of restored data in the backup block is completed (YES in steps S 503  and S 502 ). When the arrangement of the restored data in the backup block is completed, the control unit  101  interrupts the normality diagnosis processing currently being executed, and performs the normality diagnosis of the group for which the normality diagnosis was skipped. (step S 504 ). When a retryable error is detected in S 504 , the control unit  101  returns the processing to S 504 . 
     The control unit  101  determines whether or not the head address information of a faulty memory cell is set in the focused-on address (No insteps S 505  and S 502 ). The control unit  101  resumes the normality diagnosis interrupted in S 504  (YES is steps S 506  and S 505 ). The control unit  101  determines whether or not all of the normality diagnoses targeted at the head block for each group are completed (No is steps S 507  and S 505 ). The control unit  101  performs the normality diagnosis on the memory cell having the address specified by the focused-on address (NO in steps S 508  and S 507 ). The control unit  101  determines whether or not the response of the normality diagnosis from the management  115  is a notification of a retryable error (step S 509 ). The control unit  101  skips the normality diagnosis of the group that includes the faulty block, and continues the normality diagnosis of the group that does not include the faulty block until the arrangement of the restored data in the backup block is completed (YES in steps S 510  and S 509 ). When the arrangement of the restored data in the backup block is completed, the control unit  101  interrupts the normality diagnosis currently being executed, and performs the normality diagnosis of the group for which the normality diagnosis processing is skipped (step S 511 ). When S 511  is terminated, the control unit  101  returns the processing to S 505 . The control unit  101  sets the head address of the next memory cell as the focused-on address (NO insteps S 512  and S 509 ). The control unit  101  determines the head address of the next memory cell by a command such as Line_shift. When S 512  is terminated, the control unit  101  returns the processing to S 505 . The control unit  101  terminates the normality diagnosis processing (YES in steps S 513  and S 507 ). 
       FIGS. 10A and 10B  are each a flowchart explaining an example of the normality diagnosis processing performed until the arrangement of restored data in the backup block is completed. The flowcharts in  FIGS. 10A and 10B  are each a flowchart explaining in detail the processing in S 503  in  FIG. 9A . The control unit  101  counts the number of notifications of the retryable error from the management unit  115  (step S 601 ). The control unit  101  determines whether or not the number of notifications of the retryable error has reached a predetermined threshold value (step S 602 ). The control unit  101  determines that the SSD is faulty, and suspends the use of the faulty SSD (YES insteps S 603  and S 602 ). 
     The control unit  101  stores the information on the head address of the memory cell in which the retryable error is detected in an ERR_TBL (NO in steps S 604  and S 602 ). The control unit  101  determines whether or not the arrangement of the restored data in the backup block is completed (step S 605 ). The completion of the restored data in the backup block is determined by referring to, for example, a log of the SSD. The control unit  101  sets the head address of the head block of the next address as the focused-on address (step S 606 ). The control unit  101  performs the normality diagnosis on the memory cell having the address specified by the focused-on address (step S 607 ). The control unit  101  determines whether or not the response of the normality diagnosis from the management unit  115  is a notification of the retryable error (step S 608 ). The control unit  101  repeats the processing from S 602  (YES in step S 608 ). The control unit  101  adds 1 to the number of the requests for confirming whether or not the arrangement of the data in the backup block is completed (NO in steps S 609  and S 608 ). The control unit  101  sets the head address of the next memory cell as the focused-on address (step S 610 ). The control unit  101  performs the normality diagnosis on the memory cell having the address specified by the focused-on address (step S 611 ). The control unit  101  determines whether or not the response of the normality diagnosis from the management unit  115  is a notification of the retryable error (step S 612 ). The control unit  101  repeats the processing from S 602  (YES in step S 612 ). The control unit  101  determines whether or not the arrangement of the restored data in the backup block is completed (NO in steps S 613  and S 612 ). The control unit  101  repeats the processing from S 609  (NO in step S 613 ). The control unit  101  clears the value set as the focused-on address (YES in steps S 614  and S 613 ). The control unit  101  terminates the normality diagnosis processing that is executed until the arrangement of the restored data in the backup block is terminated. 
       FIG. 11  is a flowchart explaining an example of processing for performing the normality diagnosis on a group for which the normality diagnosis was skipped. The control unit  101  performs the normality diagnosis at first on a memory cell in which the retryable error is detected by using the ERR_TBL (step S 701 ). The control unit  101  determines whether or not the response of the normality diagnosis from the management unit  115  is a notification of the retryable error (step S 702 ). The control unit  101  skips the normality diagnosis of the group that includes the faulty block, and continues the normality diagnosis of the group that does not include the faulty block until the arrangement of the restored data in the backup block is completed (YES in steps S 703  and S 702 ). The control unit  101  sets the memory cell that includes the head address of the next memory cell as the next diagnosis target (NO in steps S 704  and S 702 ). The control unit  101  determines whether or not all the diagnoses of the group for which the normality diagnosis was skipped are completed (step S 705 ). The control unit  101  repeats the processing from S 701  (NO is step S 705 ). The control unit  101  determines that the ERR_TBL used in S 701  does not have the address of another ERR_TBL (step S 706 ). The control unit  101  selects another ERR_TBL and sets it as the next target for the normality diagnosis (step S 707 ). When S 707  is terminated, the control unit  101  repeats the processing from S 701 . The control unit  101  initializes the ERR_TBL (YES in steps S 708  and S 706 ). The control unit  101  executes processing from S 505  when the processing in S 708  is terminated. 
     As described above, in the method related to the embodiments, an error is detected once from the normality diagnosis on a group that includes a faulty block by skipping the normality diagnosis processing on the group that includes the block in which a failure is detected. As a result, even when a faulty block is diagnosed, since normality diagnoses are not performed a plurality of times on the faulty block, error detection is not performed a plurality of times on one block. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.