JP2004158029A - File control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always respond to an instruction for reading a home address at a high speed regardless of whether or not object data are stored in a cache memory, and to lower occurrence probability of errors. <P>SOLUTION: In an FCU 2 having the cache memory 24 for controlling a DASD 3, a storage part of a defect alternation information table 27 is formed in a memory part of the FCU 2; all the defective track regions of the DASD 3 under control are read in turning power on or resetting it; whether or not a defect alternation link is created by a flag stored in a home address part of each track is determined; the result thereof is stored in the memory part as the information table 27; and when the read instruction of the home address is received, whether or not the information table 27 is valid is determined. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a file control device such as a disk control device for performing asynchronous transfer in which a path of a channel transfer and a direct access storage device (DASD), which are an upper-level device, operates independently in time.

  7A and 7B are explanatory diagrams of a conventional example. FIG. 7A illustrates a CKD format, and FIG. 7B illustrates a method of emulating a CKD track on an FBA track.

  2. Description of the Related Art Conventionally, a method of storing data in a direct access storage device (DASD) which is an external storage device such as a magnetic disk device or an optical disk device is a CKD format which is a variable length system, and a higher-level device (OS: operating system) is used. , DASD is also a CKD format.

  In FIG. 7A, a track m on a CKD format disk includes an index (Index), a home address HA, a record (Record) 0, a record 1, a record 2,... A record k.

  The index is a track start marker. The home address HA indicates a track state and the like, and includes a flag (Flag), a track address (Track Address: cylinder number and head number), and an error correction code (Error Correction Code: ECC). This flag (Flag) indicates a use state of whether or not the track is defective, and is composed of, for example, 2 bits. The target track is “00” if the target track is normal, “10” if the target track is defective, and “01” if the target track is a replacement track. It is to be. The error correction code ECC is for data check.

  Record 0 is a record that cannot be used by the user, and records the address of a replacement track when a defective track occurs in the count section. Records 1 to k are records that can be used by the user, and each include three fields of a count part C, a key part K (sometimes omitted), and a data part D. The count section C contains the lengths of the key section K and the data section D following the count section C. The key portion K contains a key which is a marker for searching the data portion D or the like. The data part D is a part for recording data.

  However, in recent years, the real storage medium has been changed from a variable-length CKD format DASD to a fixed-length FBA format DASD, and a RAID (RAID) technique for improving reliability by adding redundant information has been used. There is a growing tendency to.

  In this case, since the format issued by the host device (OS) and the format of the actual DASD are different, the file control device (hereinafter referred to as “FCU”) emulates (converts) the CKD format on the FBA format DASD. (CKD On Fba = COF) When this COF technology is used, a track in CKD format is emulated on a real DASD in FBA format as shown in FIG.

  In FIG. 7B, the upper diagram shows one track in the FBA format. In this example, there are blocks n, block n + 1, block n + 2, block n + 3, block n + 4, block n + 5,. This one block can include 0 to 8 records in CKD format.

  For example, if one track of the CKD format uses blocks n to n + 15 (for 16 blocks) of the FBA format, the upper diagram of FIG. 7B looks like the lower diagram. That is, in one track of the FBA format, the emulated track of the CKD format is track m (FBA blocks n to n + 15), track m + 1 (FBA blocks n + 16 to n + 31), track m + 2 (FBA blocks n + 32 to n + 47), and track m + 3 (FBA blocks). Blocks n + 48 to n + 63) and tracks m + 4 (FBA blocks n + 64 to n + 79) are provided for about five tracks.

  Conventionally, in the write operation, in order to speed up the processing, when a write request is made from a higher-level device, the data to be written is not written to DASD, and the nonvolatile memory (FCU) in the file control unit (FCU) is not written. A method of writing data only to NVS (Non Volatile Storage) and writing back to DASD using the idle time of the FCU (high-speed writing mechanism for DASD) has been considered.

  Further, as a method of writing back data from NVS to DASD by improving this method, a method of writing back a plurality of continuous tracks to DASD in one event (multi-track destage) is considered.

  However, in a file subsystem using the COF technique, destaging of a continuous track does not necessarily expect an improvement in performance. This is because two consecutive tracks in the CKD format become adjacent blocks in the FBA format, and the FCU based on one-track processing in the CKD format performs post-processing after writing back the track. This is because the leading portion of the following track passes by, causing one rotation wait.

  Referring to FIG. 7, for example, when the conventional CKD format DASD is used, the time from the destage of the track m until the head of the DASD arrives at the home address HA of the track m + 1 is the record of the track m. After the processing of k is completed, this is the time from when the head passes through the index to when the head is further positioned at the home address HA of the track m + 1.

  However, when the COF technique is used, only time corresponding to the inter-block gap G is given from the end of the processing of the track m to the start of the processing of the track m + 1. Logically, this time alone does not allow the FCU to complete the track end processing such as error checking and the subsequent track start processing. For this reason, the head waits for the disk to make one rotation and to be positioned again at the head of track m + 1 (block n + 16 in the FBA format).

  In general, when a target data is stored in the cache memory, a response to the entire read command (Read Command), which is a read command from the higher-level device, is read from the cache memory and responded, and the target data is stored in the cache memory. If not, access to the actual DASD occurs, and the time for positioning the head on the DASD and waiting for rotation is spent.

  The above-mentioned conventional one has the following problems.

  (1) A problem that the multitrack destaging method, which is a method for eliminating the rotation wait of the DASD by continuously destage, uses the COF technology, the rotation wait occurs, and the function is not fulfilled. was there.

  (2) Even when the target data is stored in the cache memory, the response to the general read command from the host device consumes the time for performing the hash conversion for obtaining the storage location and the operation for reading from the cache memory. Also, the probability of occurrence of an access error due to a hardware failure or the like has been increased.

  SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problem and does not continuously process a logical CKD destage track to a DASD, but secures sufficient time for post-processing and pre-processing of a track, thereby enabling useless rotation. High-speed destage without waiting, and can always respond to a home address read instruction (Read HA instruction) at high speed regardless of whether or not the target data is stored in the cache memory, and can generate an error. The purpose is to lower the probability of occurrence.

  The present invention is configured as follows in order to solve the above problem.

  FIG. 1 is a view for explaining the principle of the present invention. In FIG. 1, reference numeral 1 denotes a host device, 2 denotes a file control unit (FCU), 3 denotes a direct access storage device (DASD), 20 denotes a memory unit, and 21 denotes a channel adapter (CA). , 22 denotes a device adapter (DA), 23 denotes a cache management unit (CFE), 24 denotes a cache memory, 25 denotes a nonvolatile memory (NVS), and 27 denotes a defective replacement information table.

  In the FCU 2 having the cache memory 24 for controlling the DASD 3, a storage unit for the defect replacement information table 27 is provided in the storage unit of the FCU 2, and when the power is turned on or reset, the defective track areas of all the subordinate DASDs 3 are read out. Based on the flag stored in the home address section of each track, it is determined whether or not a defective replacement link has been created. The result is stored in the storage section as a defective replacement information table 27, and a home address read command has been received. In this case, it is determined whether the defective replacement information table 27 is valid. For this reason, it is possible to prevent a response with invalid invalid replacement information table information.

  If the result of the determination indicates that the defective replacement information table 27 is invalid, the target home address is read from the cache memory 24 if it exists on the cache memory 24, and read from the DASD 3 if it does not exist. When the defective replacement information table 27 is valid, the defective replacement link information in the defective replacement information table 27 is referred to, and the flag information which is a part of the response to the read instruction of the received home address is read. Determine. Therefore, a response to the flag information can be made even when the defective replacement information table 27 is invalid, and when it is valid, the flag information can be created at high speed.

  Further, complete response information to the read instruction of the home address is created from the determined flag information and the track address which is a part of the response to the read instruction of the home address using the already received seek address. Therefore, it is possible to quickly respond to a read instruction of the home address when the defective replacement information table 27 is valid.

  When the DASD 3 is a fixed-length array disk and the FCU 2 is emulating a variable-length system with the array disk, a track defect which is a part of a response to a home address read command including additional information is performed. The information is fixed to a standard value, and response information to a read instruction of a home address including complete additional information is created from the flaw information, the flag information, and the track address. Therefore, the response to the read instruction of the home address including the additional information when the defective replacement information table 27 is valid can be performed at high speed without accessing the cache memory or the like, and the error occurrence probability can be reduced. it can.

  According to the present invention, the following effects can be obtained.

  (1) The FCU reads the defective track areas of all the subordinate DASDs 3 when the power is turned on or resets, and determines whether a defective replacement link has been created based on a flag stored in the home address section of each track. Then, the result is stored in the storage unit as a defective replacement information table, and when a read instruction of a home address is received, a response is made with information of an invalid defective replacement information table in order to determine whether the defective replacement information table is valid. Can be prevented.

  (2) If the FCU determines that the defective replacement information table is invalid, the home address is read from the cache memory if the target home address is present in the cache memory, and is transferred from the DASD 3 if the target home address is not present. When the replacement information table is valid, the defective replacement information table 27 is referred to by referring to the defective replacement link information in the defective replacement information table and determining flag information that is a part of the response to the read command of the received home address. The flag information can be responded to even when it is invalid, and the flag information can be created at high speed when it is valid.

  (3) To create complete response information to a home address read command from the determined flag information and a track address that is part of a response to a home address read command using a previously received seek address. In addition, it is possible to quickly respond to a read instruction of the home address when the defective replacement information table is valid.

  (4) When the FCU emulates the variable length system on the array disk, the defect information of the track, which is a part of the response to the read instruction of the home address including the additional information, is determined to a standard value, and the defect information and the defect information are determined. A response to the read instruction of the home address including the additional information when the defective replacement information table is valid is created by caching the response information to the read instruction of the home address including the complete additional information from the flag information and the track address. This can be performed at high speed without accessing a memory or the like, and the error probability can be reduced.

  2 and 3 are views showing a first embodiment of the present invention, and FIGS. 4 to 6 are views showing a second embodiment of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Description of First Embodiment]
1): Description of File Control Unit (FCU) FIG. 2 is an explanatory diagram of the file control unit. The file control unit (FCU) 2 reads / writes data from / to the DASD 3 in accordance with an instruction from a host device. It is connected to a host device by a channel adapter (CA) 21, and is connected to a DASD adapter 31 of DASD 3 such as a disk array by a device adapter (DA) 22. Further, the FCU 2 is provided with a service adapter (SA) 26 connected to the hard disk (HD) 4.

  In the FCU 2, a channel adapter 21, a device adapter 22, a cache management unit 23, a cache memory 24, and a non-volatile memory (NVS) 25 are provided.

  A plurality of channel adapters 21 are provided, mainly controlling an interface with a channel of a higher-level device, and a device adapter 22 controls an interface with the DASD 3. The cache management unit 23 manages tracks and the like registered in the cache memory 24.

  The cache memory 24 is a buffer storage device that holds a copy of commands and data on the DASD 3 which are likely to be used later. The nonvolatile memory 25 is backed up by a battery so that data is not lost even when the power is turned off.

  The service adapter 26 performs initial setting of the file control device, management of the history of error information of the file device, and the like based on information from the hard disk 4. The DASD 3 is an FBA format (fixed length type) storage device such as a disk array using RAID technology. The DASD adapter 31 controls an interface with the FCU 2.

2): Description of operation of file control device When FCU 2 receives an instruction to write data to DASD 3 from the host device, FCU 2 converts the CKD format from the host device to FBA format by channel adapter 21, and cache memory 24 and nonvolatile memory 25, a high-speed writing process is performed.

  When detecting that the track generated by the high-speed writing mechanism exists in the nonvolatile memory 25, the cache management unit 23 searches whether or not there is a continuous track among all the tracks. Here, the cache management unit 23 calculates track intervals at which continuous destaging is possible, and requests the device adapter 22 to perform destaging using the head track, the end track to be destaged, and the destage track interval as information.

  The device adapter 22 that has received the destage request issues a selection command for positioning the head to the DASD 3 with respect to the first track based on the information.

  After the selection of the DASD 3 is completed, the device adapter 22 determines a track to be destaged based on the information received from the cache management unit 23.

  The first track to be destaged is the head track notified from the cache management unit 23, and the next track to be destaged is a track obtained by adding the destage track interval to the head track. The next track to be destaged is a track obtained by adding the destage track interval to the current destage track.

  The device adapter 22 repeats the above operation, and repeats the above operation until the end track address notified from the cache management unit 23 is exceeded.

  Note that the destage track interval is an interval for skipping the destage target track by an amount sufficient to secure sufficient time for post-processing and pre-processing of the track. In the conventional multi-track destaging, useless rotation waits corresponding to the number of destage tracks have occurred. However, use of this embodiment eliminates useless rotation waits.

3): Description of specific example of destage operation FIG. 3 is an explanatory diagram of a destage target track.

  The cache management unit 23 detects that the non-volatile memory 25 has a track to be destaged. In this case, it is assumed that there are 15 target DASDs 3 in one cylinder, and the destage target track is as shown in FIG. Further, if it is assumed that post-processing and pre-processing of the track can be completed with the rotation time of three tracks for the target DASD 3, the continuous destage track interval is calculated to be 4.

  Here, the tracks to be destaged this time are the tracks marked with a circle in the first column and the tracks marked with a circle in the second column in FIG.

  (1): The cache management unit 23 searches for a destage track. As a first time, the first track (0) = cylinder value “0005” / head value “0000”, and the end track (+20) = cylinder value “0006” The destage is issued to the device adapter 22 with the head value “0005” and the continuous destage track interval = 4.

  (2): Upon receiving the destage request from the cache management unit 23, the device adapter 22 performs DASD3 selection for the cylinder value “0005” and the head value “0000” that are the track (0).

  (3): After the selection of the DASD 3 is completed, the device adapter 22 sequentially tracks the circles (+4), (+8), and (+12) from the first track (0) in the first column in FIG. (+16) is destaged, and after the destage of the end track (+20) is completed, the completion of the continuous destage processing is reported to the cache management unit 23.

  (4): For the second time, the cache management unit 23 determines that the first track (+11) = cylinder value “0005” / head value “000B”, the ending track (+23) = cylinder value “0006”, the head value “0008”, The destage is issued to the device adapter 22 with the continuous destage track interval = 4.

  (5): Upon receiving the destage request from the cache management unit 23, the device adapter 22 performs DASD3 selection for the cylinder value “0005” and the head value “000B” that are the track (+11).

  (6): After the selection of DASD3 is completed, the device adapter 22 destages the tracks (+15) and (+19) marked with ● in order from the first track (+11) in the first column in FIG. Then, after the destage of the end track (+23) is completed, the completion of the continuous destage processing is reported to the cache management unit 23.

  In the above-described embodiment, the continuous destage track interval is set to 4, but the cache management unit 23 determines the type of the destage target DASD 3 and calculates the continuous destage track interval based on the performance of the target DASD 3. Usually, pre-processing and post-processing of a track can be performed while skipping one track. In this case, the continuous destage track interval is 2.

  Further, by storing the number of continuous destage tracks in the hard disk 4 or the like in advance, the number of continuous destage tracks can be defined in advance by initial setting of the FCU. Thereby, the cache management unit 23 extracts continuous tracks that can be destaged from the predefined number of continuous destage tracks.

  Then, the cache management unit 23, when extracting continuous tracks that can be destaged, delays the destage if the number of the continuous tracks that can be destaged is smaller than a predetermined number of continuous destage tracks, If the number is larger than the predetermined number of continuous destage tracks, the device adapter 22 is requested to destage the predetermined number of continuous destage tracks.

  Further, the device adapter 22 compares the number of tracks destaged by the continuous destage with the number of continuous destage tracks defined in advance after the end of the continuous destage processing, and when the comparison value is different, A mechanism is provided for notifying the cache management unit 23 that a logical inconsistency has been detected, and a mechanism for notifying the cache management unit 23 that destaging has been completed normally when the comparison values are equal. Provide.

[Description of Second Embodiment]
1): Description of File Control Unit (FCU) FIG. 4 is an explanatory diagram of the file control unit in the second embodiment. The file control unit (FCU) 2 reads / writes data from / to the DASD 3 in accordance with an instruction from a host device. It is connected to a higher-level device by a channel adapter (CA) 21 and is connected to a DASD adapter 31 of DASD 3 by a device adapter (DA). Further, the FCU 2 is provided with a service adapter (SA) 26 connected to the hard disk (HD) 4.

  In the FCU 2, a channel adapter 21, a device adapter 22, a cache management unit 23, a cache memory 24, and a non-volatile memory (NVS) 25 are provided.

  A plurality of channel adapters 21 are provided, mainly controlling an interface with a channel of a higher-level device, and a device adapter 22 controls an interface with the DASD 3. The cache management section 23 manages tracks and the like registered in the cache memory 24, and has a storage section provided with a place for storing the defect replacement information table 27.

  The cache memory 24 is a buffer storage device that holds a copy of commands and data on the DASD 3 which are likely to be used later. The nonvolatile memory 25 is backed up by a battery so that data is not lost even when the power is turned off.

  The service adapter 26 performs initial setting of the file control device, management of the history of error information of the file device, and the like based on information from the hard disk 4. The DASD 3 is a storage device including a plurality of devices such as a disk device and an optical disk device. The DASD adapter 31 controls an interface with the FCU 2.

2): Description of defective replacement information table FIG. 5 is an explanatory diagram of the defective replacement information table. FIG. 5A illustrates the defective replacement information table, and FIG. 5B illustrates one set of the defective replacement information. It is.

  In FIG. 5A, in this example, defective replacement information per device can be stored up to a maximum of 45 tracks, such as set numbers 0 to 44 at the left end. One set of the defective replacement information has a storage unit for 4 bytes on each of the defective side and the replacement side. Further, the defective replacement information table 27 is provided with storage units for the maximum number of connectable devices (256 devices in this example).

  In FIG. 5B, one set of defective replacement information is divided into a defective side and a replacement side. The defective side is provided with storage units for cylinder values, head values, and information, and the replacement side is provided with storage units for cylinder values, head values, and device values (device numbers). In the storage of this information, for example, if “40” is stored, it indicates that the replacement side is valid. If “20”, it indicates that the defective side is valid. For example, this indicates that both the defective side and the replacement side are valid, that is, the link has been established.

3): Description of Home Address Read Instruction (Diag Read HA Command) including Additional Information In this embodiment, the defect replacement information table 27 in the file control unit (FCU) 2 has the defect replacement information of all DASDs 3 under its control. Is stored. This defective replacement information is created and updated at the time of processing of writing the home address (Write HA) or writing of the home address including additional information (Diag Write HA).

  The data transferred by the home address read command (Dialog Read HA Command) including the additional information includes a flag (Flag), a track address (Track Address), flaw information, a cell (Cell) value, and a physical track address.

  In this embodiment, since the defective replacement information of the track is stored in the FCU 2, the flag information of the home address HA section can be created by the FCU 2. Since the track address and the physical track address are physical positions of the track, they should match the seek value, which can be created in the FCU 2.

  When an array disk using the RAID technology is considered, the scratch information is a standard value with no scratches, and there is no problem. The cell value indicates the distance from the index, and is a fixed value when there is no scratch on the track.

  The data transferred by the home address read instruction (Read HA Command) is a flag and a track address, and is part of the information required by the home address read instruction (Diag Read HA Command) including additional information. Again, it can be created in FCU2.

  By storing the defect replacement information in the FCU 2 in this way, the Read HA Command and the Diag Read HA Command are always accessed without accessing the real DASD 3 or without reading data from the cache memory. , Target information can be transmitted.

4): Description of Operation of File Control Unit (FCU) The operation of the FCU 2 will be described below.

  (1): When the power of the FCU 2 is turned on or reset, the FCU 2 (cache management unit 23) reads the defective track areas of all the subordinate DASDs 3 and reads the defective track area according to the flag stored in the home address HA section of each track. It is determined whether or not a defective replacement link has been created, and the result is stored as a defective replacement information table 27 in a memory (storage unit) in the FCU 2.

  (2): In order to issue a read instruction for DASD3 access, a seek instruction for specifying a target track must be issued in advance. Therefore, the FCU 2 can recognize the target track address from the seek command issued from the channel of the higher-level device prior to the read command.

  (3): When the FCU 2 receives a read instruction (Read HA Command) for the home address of the subordinate DASD 3 from the channel of the higher-level device, the FCU 2 determines whether the defective replacement information table 27 is valid.

  (4): If the result of this determination indicates that the defective replacement information table 27 is invalid (for example, failure to read the defective track information from the home address HA of the DASD 3), the FCU 2 stores the flag information of the target home address HA. Since data cannot be confirmed, the data is read from the cache memory 24 if the data exists in the cache memory 24, and from the DASD 3 if the data does not exist, and the normal read operation is performed.

  (5): If the result of the determination indicates that the defective replacement information table 27 is valid, the defective replacement link information in the defective replacement information table 27 is referred to to determine whether a defective replacement link has been created in the target track. (Determine whether the track is a defective track, a replacement track, or a normal track).

  (6): If a defective replacement link has been created, the corresponding bit is set in the flag area of the home address HA section. Further, since the cylinder head value which is the track address of the home address HA section always coincides with the physical cylinder head value, by setting the value already specified by the seek instruction, the cache memory can be used without using the cache memory. , Can respond with appropriate value.

  (7): The data to be transferred by the FCU 2 with the read instruction of the home address including the additional information (Diag Read HA Command) is converted into the data transferred by the read command of the home address (Read HA Command) described above. It is obtained by adding the scratch information of the track and the cell value. However, in the FCU 2 using an array disk (FCU using COF technology), the flaw information can always be specified to a standard value, so that such information can be created inside the FCU 2. Therefore, the FCU 2 can also transfer an appropriate value to the Diag Read HA Command.

  FIG. 6 is a processing flowchart for the Read HA Command. Hereinafter, description will be made in accordance with the processes S1 to S5 of FIG.

  S1: The FCU 2 determines whether the defective replacement information table 27 is valid when receiving the Read HA Command of the subordinate DASD 3 from the higher-level device, and determines whether the defective replacement information table 27 is valid when the defective replacement information table 27 is valid. Referring to the defective replacement link information in the table 27, it is determined whether or not the target track is a defective replacement track. If the target track is a defective replacement track, the process proceeds to step S2. If the target track is not a defective replacement track, the process proceeds to step S5. (If the defective replacement information table 27 is invalid, the cache memory 24 or DASD 3 Read and perform normal read operation.)

  S2: The FCU 2 determines whether the target track is a defective track. If the target track is a defective track, the process proceeds to step S3. If the target track is not a defective track, the process proceeds to step S4.

  S3: The FCU 2 sets the bad track information in the flag area of the home address HA section of the target track, and proceeds to processing S5.

  S4: The FCU 2 sets the replacement track information in the flag area of the home address HA section of the target track, and proceeds to processing S5.

  S5: The FCU 2 notifies the upper-level device of the defective replacement information set in the flag area and the cylinder head value as the track address, and ends this processing.

FIG. 2 is a diagram illustrating the principle of the present invention. FIG. 3 is an explanatory diagram of a file control device according to the first embodiment. FIG. 4 is an explanatory diagram of a destage target track in the first embodiment. FIG. 11 is an explanatory diagram of a file control device according to a second embodiment. FIG. 14 is an explanatory diagram of a defective replacement information table according to the second embodiment. It is a processing flowchart for Read HA Command in the second embodiment. It is explanatory drawing of a conventional example.

Explanation of reference numerals

1 Upper device 2 File control unit (FCU)
3 Direct access storage device (DASD)
20 Memory unit 21 Channel adapter (CA)
22 Device Adapter (DA)
23 Cache Management Unit (CFE)
24 Cache memory 25 Non-volatile memory (NVS)
27 Bad replacement information table

Claims (4)

In a file control device having a cache memory for controlling a direct access storage device,
A storage unit for the defective replacement information table is provided in a storage unit of the file control device,
At power-on or at reset, read the defective track areas of all the subordinate direct access storage devices, and determine whether a defective replacement link has been created by the flag stored in the home address section of each track, The result is stored in the storage unit as a defective replacement information table,
A file control device which, when receiving a home address read command, determines whether the defective replacement information table is valid. As a result of the judgment,
If the defective replacement information table is invalid, the target home address, if present in the cache memory, from the cache memory, if not, read from the direct access storage device and transfer the information,
When the defective replacement information table is valid, referring to the defective replacement link information in the defective replacement information table, flag information that is a part of a response to the read command of the received home address is determined. 2. The file control device according to claim 1, wherein: The determined flag information;
3. A complete response information to a home address read command is created from a track address which is a part of a response to a home address read command using a previously received seek address. File control unit. When the direct access storage device is a fixed-length array disk, and the file control device is emulating a variable-length system with the array disk,
Determine the scratch information of the track which is a part of the response to the read command of the home address including the additional information to the standard value,
4. The file control device according to claim 3, wherein response information to a read instruction of a home address including complete additional information is created from the flaw information, the flag information, and the track address.

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