JP3882467B2 - Snapshot management method for storage system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention mainly relates to a snapshot management method in an external storage system of a computer.
[0002]
[Prior art]
In general, data recorded on an external storage device of a computer such as a hard disk is regularly copied to tape so that the lost data can be recovered if the data is lost due to a device failure, software defect or incorrect operation. Must be saved (backup). At this time, if the data is updated during the copying operation and the data is inconsistent, it does not make sense as a backup. Therefore, it is necessary to guarantee the data consistency during the copying operation.
[0003]
In order to guarantee the consistency of the data to be backed up, a program other than the backup program that accesses the data may be stopped. However, in a system that requires high availability, the program cannot be stopped for a long time. Therefore, it is necessary to provide a mechanism for creating a storage image of data at the start of backup without preventing the program from updating data during backup. Here, a storage image of data at a certain time point is called a snapshot, and a mechanism that provides a state in which data can be updated while creating a snapshot at a specified time point is called a snapshot management method. In addition, creating a snapshot by the snapshot management method is called snapshot acquisition, and the data for which the snapshot is acquired is called original data. Also, quitting the state in which the snapshot has been created is called snapshot deletion.
[0004]
One conventional snapshot management method is a data duplication method.
[0005]
In this method, in a normal state where a snapshot is not acquired, a program on a computer duplexes (mirrors) all data in two storage areas. When a snapshot is acquired, duplication is stopped, the two storage areas are separated into independent areas, one area is provided as original data, and the other area is provided as a snapshot.
[0006]
While the snapshot is acquired and duplication is stopped, updating of the data in the storage area of the original data is permitted, and when the data update occurs, the updated position is recorded. When the snapshot was deleted, data duplication was resumed, and update data whose contents did not match between the two storage areas were provided as a snapshot from the storage area of the original data based on the record of the update position Copy to storage area (mirror resynchronization).
[0007]
A method of duplicating data by a program on a computer is shown in US Pat. No. 5,051,887, for example.
[0008]
[Problems to be solved by the invention]
In the snapshot management method based on data duplication, during mirror resynchronization, normal access for updating / referencing and copy access for updated data are concentrated in the storage area of the original data, and the performance of normal access deteriorates. Since the time required for mirror resynchronization is proportional to the amount of data updated while taking a snapshot and stopping duplexing, assuming that update access occurs the same number of times per unit time, mirror resynchronization The time required for conversion increases in proportion to the stoppage time of duplexing. When taking a backup from a snapshot, a copy is made to a relatively low-speed tape or the like through a computer. There is a problem that the synchronization time becomes long.
[0009]
Further, since it is necessary to instruct deletion of the snapshot after using the snapshot, a program for managing the timing for starting the snapshot deletion program upon completion of the backup is required, which complicates the backup program. There is a problem that the development period of the program becomes longer corresponding to the complexity, the price increases, and the system to be configured becomes expensive.
[0010]
The first object of the present invention is to reduce the amount of copy of update data during mirror resynchronization and reduce performance by shortening the time during which snapshots are acquired and duplexing is stopped. It is to provide a snapshot management method that shortens the conversion time.
[0011]
A second object of the present invention is to simplify a backup program by omitting a snapshot deletion instruction after using a snapshot, and to provide a snapshot management method with an inexpensive system.
[0012]
[Means for Solving the Problems]
In order to achieve the first object, the present invention provides a temporary LU in a disk array as a temporary temporary area in a snapshot management method using data duplication. The temporary LU is a high-speed disk and can reduce the time during which duplication is stopped by taking a snapshot.
[0013]
In order to achieve the second object, the present invention provides a temporary LU in a disk array as a temporary temporary area in a snapshot management method using data duplication. By saving the snapshot in the temporary LU, the snapshot deletion process is unnecessary.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
The first embodiment of the present invention reduces the copy amount of original data when performing mirror resynchronization by shortening the time during which duplication is stopped in the snapshot management method using data duplication. This is to shorten the mirror resynchronization time in which the data access performance from the database program is lowered.
[0015]
In addition, the backup program is simplified by omitting a snapshot deletion instruction after using the snapshot.
[0016]
In the present invention, a backup is taken as an example of using a snapshot, but it can also be used for other purposes such as OLAP (OnLine Analytical Processing) and system testing.
[0017]
(1) Description of configuration
The system configuration of the first embodiment of the present invention will be described with reference to FIG. In FIG. 1, a computer 100 and a disk array 200 are connected by a SCSI bus 300 via SCSI interfaces 140 and 240. The memory 120 of the computer 100 includes a database program 126 and a backup program 127 that are executed by the CPU 110 that controls the computer 100. The disk array 200 includes disks 251 to 253 controlled by the disk controller 250, and a snapshot management program 221 is stored in the memory 220 and is executed by the CPU 210. Note that the disks 251 to 253 may be virtual disks, or each may be an array composed of two or more disks.
[0018]
The storage area in each of the disks 251 to 253 is accessed from a computer as an LU (Logical Unit) which is a SCSI logical unit. The storage areas corresponding to the disks 251 to 253 are LU 261 to 263, respectively. In this embodiment, the snapshot management program 221 in the disk array 220 manages the LU 261 and LU 262 in a duplex manner, the LU 261 is used as a mirror source LU having original data, and the LU 262 is a mirror destination LU that is a mirror of the original data. And The LU 263 is a temporary LU that is a temporary copy destination when a snapshot is acquired, and the copy source is the LU 262.
[0019]
Next, a program in the computer 100 will be described.
[0020]
The database program 126 has a function of accessing the LU 261 that is the mirror source LU during execution and switching to a backup mode that controls data update and ensures data consistency in the LU 261. Transition to the backup mode is made in accordance with an instruction from the user or the backup program 127. The backup program 127 has a function of reading data for backing up to a tape or the like from the LU 263, which is a temporary LU storing a snapshot in accordance with an instruction from the user, a function of issuing a SCSI ModeSelect command to the disk array 200, and a database program. 126 has a function of instructing validation / invalidation of the backup mode.
[0021]
Next, programs and management tables in the disk array 200 will be described.
[0022]
The snapshot management program 221 of the disk array 200 has a disk access subprogram 230 for instructing disk access to the disk controller 250 in response to a request from the computer 100 and another update designated in advance by duplicating updates to one LU. This also applies to LUs, and has an LU mirror subprogram 231 that writes the same contents to two LUs. For example, in this embodiment, access to the LU 261 is duplicated in the LU 262. Further, the snapshot management program 221 temporarily copies original data from the mirror destination LU to the temporary LU (temporary copy) when acquiring the snapshot, and the copy completion position is stored in a copy position management table 223 described later. Temporary copy subprogram 233 to be recorded, non-mirror update monitoring subprogram 234 for detecting an update to the mirror source LU when duplexing is stopped (during non-mirroring), and the update position to be described later in non-mirroring It has a non-mirrored update position management subprogram 235 that is recorded in the update position management table 222, and a mirror resynchronization subprogram 232 that copies the updated part of the mirror source LU to the mirror destination LU when performing mirror resynchronization.
[0023]
The non-mirror update position management table 222 records the update position of the mirror source LU updated at the time of non-mirror, and one update position management table is provided for each mirror source LU. The non-mirror update position management table 222 is a bitmap as shown in FIG. 2, and includes all LBA set numbers and update states in the mirror source LU. An LBA set is an individual set when the entire area of an LU is divided from the top in units of one or more equal numbers of LBAs (Logical Block Address), and the LBA set number is the top of the LBA. A serial number is assigned to each LBA set from the side. The update state indicates whether or not the LBA set has been updated, and designates 1 and 0 respectively according to “update” and “non-update”. The initial setting value of the update state is 0. The example of FIG. 2 shows a state in which only the area of LBA set number 1 is updated at the time of non-mirroring.
[0024]
The copy position management table 223 records the update position where copying from the mirror destination LU to the temporary LU has been completed at the time of temporary copy, and one copy position management table 223 is provided for each mirror destination LU. The copy position management table 223 is a bitmap as shown in FIG. 3 and includes all LBA set numbers and copy states in the mirror destination LU. The definition of the LBA set number is the same as that of the non-mirror update position management table 222. The copy status indicates whether or not the LBA set has been copied, and designates 1 and 0 according to “copy incomplete” and “copy complete”, respectively. The initial setting value for the copy status is 1. In the example of FIG. 3, it is shown that the area of LBA set numbers 0 and 1 has been copied. Note that the update state of the non-mirror update position management table 222 and the specified value of the copy state of the copy position management table 223 are 0 when the data matches between the LUs being compared, and they do not match. Can be paraphrased as 1.
[0025]
(2) Acquisition of snapshot
The operation of the backup program 127 and the snapshot management program 221 at the time of acquiring a snapshot will be described with reference to the flowchart of FIG. 4, taking as an example the case where a snapshot of the mirror source LU 261 is provided as the temporary LU 263.
[0026]
First, the backup program 127 of the computer 100 gives an instruction to the database program 126, and validates the backup mode to guarantee the consistency of the data for acquiring the snapshot (step 2000). Next, the backup program 127 issues a ModeSelect command for acquiring a snapshot to the disk array 200 (step 2001). Upon receipt of the ModeSelect command (step 3000), the snapshot management program 221 of the disk array 200 enables the non-mirror update monitoring subprogram 234 and the non-mirror update location management subprogram 235, and starts recording the update location of the LU 261. (Step 3001). Thereafter, when the LU 261 is updated, 1 is set in the update state of the LBA set including the updated LBA in the non-mirror update position management table 222, and the fact that there has been an update is recorded. Next, the snapshot management program 221 invalidates the LU mirror subprogram 231 and stops duplication of the LU 261 and LU 262 (step 3002). As a result, the update to the LU 261 that is the mirror source LU is not reflected in the LU 262 that is the mirror destination LU. Next, the snapshot management program 221 transmits the completion status of the ModeSelect command to the backup program 127 of the computer 100 (step 3003). When the backup program 127 receives the completion status of the ModeSelect command (step 2002), it gives an instruction to the database program 126 and invalidates the backup mode (step 2003).
[0027]
Next, the backup program 127 issues a ModeSelect command for instructing the disk array 200 to start temporary copy for saving a snapshot in the LU 263 (step 2004). When receiving the ModeSelect command (step 3004), the snapshot management program 221 of the disk array 200 validates the temporary copy subprogram 233, and copies data from the LU 262 that is the mirror destination LU to the LU 263 that is the temporary LU. For the LBA set for which copying has been completed, the copy status in the copy position management table 223 is set to 0, and it is recorded that copying has been completed (step 3005). For data copying, the READ command is issued to the disk 252 including the LU 262 to read the specified LBA data, the WRITE command is issued to the disk 253 including the LU 263, and the data read to the same LBA as the LBA specified to the LU 262 is read. Implement by writing. This is performed for all areas of the LU 262 and LU 263. The COPY command may be used to copy the data. When the data copy is completed, the snapshot management program 221 validates the LU mirror subprogram 231 and resumes the duplication of the LU 261 and LU 262 (step 3006). Thereby, the update to the LU 261 is reflected in the LU 262. Next, the snapshot management program 221 invalidates the non-mirror time update monitoring subprogram 234 and the non-mirror time update position management subprogram 235, and stops the LU 261 update position recording (step 3007). Thereafter, the non-mirrored update position management table 222 is not changed. Next, the snapshot management program 221 validates the mirror resynchronization subprogram, refers to the non-mirror update position management table 222, and copies the portion where the contents do not match between the LU 261 and LU 262 from the LU 261 to the LU 262 (step). 3008). Next, the snapshot management program 221 transmits the completion status of the ModeSelect command to the backup program 127 of the computer 100 (step 3009). The backup program 127 receives the end status of the ModeSelect command and ends the operation (step 2005).
[0028]
Here, the operation of the mirror resynchronization subprogram 232 for copying data from the LU 261 to the LU 262 in step 3008 will be described with reference to the flowchart of FIG. First, the mirror resynchronization subprogram 232 checks whether there is 1 as an update record in the non-mirror update position management table 222 (step 1001). If there is no update record 1, mirror resynchronization is complete and the process ends (step 1002). If there is an update record, the update of the corresponding recording position is suppressed (step 1003), and the data at the corresponding recording position is copied from the LU 261 which is the mirror source LU to the LU 262 which is the mirror destination LU (step 1004). For data copying, the READ command is issued to the disk 251 including the LU 261 to read the specified LBA data, the WRITE command is issued to the disk 252 including the LU 262, and the data read to the same LBA as the LBA specified to the LU 261 is read. Implement by writing. The COPY command may be used to copy the data. Next, the mirror resynchronization subprogram 232 releases the update suppression of the corresponding recording position (step 1005), sets the corresponding update record in the non-mirror update position management table 222 to 0, and deletes the update record ( Step 1006) and return to Step 1001.
[0029]
The above is the operation of the backup program 127 and the snapshot management program 221 when acquiring a snapshot.
[0030]
(3) Computer operation when reading and writing data and reading snapshots
First, the operation of the database program 126 when the computer 100 accesses the data of the LU 261 in the disk array 200 will be described. The database program 126 performs the same operation regardless of whether or not a snapshot is acquired.
[0031]
When the database program 126 reads LU 261 data, the database program 126 issues a READ command for reading the LU 261 data to the disk array 200. Finally, the database program 126 receives data and status from the disk array 200 and ends the operation. When the database program 126 writes data to the LU 261, the database program 126 issues a WRITE command for writing data to the LU 261 to the disk array 200, and transmits the data. Finally, the database program 126 receives the status from the disk array 200 and ends the operation.
[0032]
Next, the operation of the backup program 127 when the computer 100 reads a snapshot of the LU 261 in the disk array 200 will be described.
[0033]
When the backup program 127 reads the snapshot of the LU 261, the backup program 127 issues a READ command for reading the data of the LU 263, which is the temporary LU of the LU 261, to the disk array 200. Finally, the backup program 127 receives data and status from the disk array 200 and ends the operation. When the disk array 200 cannot transmit the snapshot data, only the error status is received from the disk array 200.
[0034]
(4) Disk array operation when reading and writing data and reading snapshots
First, the operation of the snapshot management program 221 when the computer 100 accesses the data of the LU 261 in the disk array 200 will be described.
[0035]
When the computer 100 reads data from the LU 261, the snapshot management program 221 receives a READ command for the LU 261. Next, if the LU mirror subprogram 231 is valid and the copy of the updated portion by the mirror resynchronization subprogram 232 has been completed, data is read from the LU 261 or the LU 262 that is the mirror destination LU. Otherwise, data is read from the LU 261. Finally, read
The received data and status are transmitted to the computer 100. If the contents of the LU 261 and the LU 262 that is the mirror destination LU match, the load can be distributed by reading data from either of them.
[0036]
When the computer 100 writes data to the LU 261 and updates the stored contents, the snapshot management program 221 receives a WRITE command and data for the LU 261. Next, if the LU mirror subprogram 231 is valid, data is written to the LU 261 and the mirror destination LU 262, and if invalid, data is written to the LU 261. Next, if the non-mirror time update monitoring subprogram 234 and the non-mirror time update position management subprogram 235 are valid, the update state of the LBA set including the LBA updated to the non-mirror time update position management table 222 of the LU 261 Set to 1 and do nothing if disabled. Finally, the status is transmitted to the computer 100.
[0037]
Next, the operation of the snapshot management program 221 when the computer 100 reads a snapshot of the LU 261 in the disk array 200 will be described.
[0038]
When the computer 100 reads a snapshot of the LU 261, the snapshot management program 221 receives a READ command for the LU 263 that is a temporary LU of the LU 261. Next, the snapshot management program 221 refers to the copy position management table 223 and checks the copy status of the LBA set including the LBA specified by the READ command. When the copy state is 0, that is, when a snapshot of the LU 261 is stored in the LU 263 that is a temporary LU, data is read from the LU 263. When the copy state is 1, that is, when the snapshot of the LU 261 is not stored in the LU 263 that is a temporary LU, data is read from the LU 262 that is a mirror destination LU. Finally, the read data and status are transmitted to the computer 100. When the snapshot data cannot be transmitted, only the error status is transmitted to the disk array 200.
[0039]
Note that during the copying of the updated portion by the mirror resynchronization subprogram 232, the copy processing and the data access processing to the LU 261 by the computer 100 are concentrated on the same LU 261, so the data access performance is degraded.
[0040]
(5) Effect
According to the present embodiment, in a snapshot management method for providing a storage area as a snapshot by stopping duplication when a snapshot is acquired, a temporary LU is used as a temporary temporary area for storing a snapshot. By providing the LU 263, the duplication stop time of the LU 261 that is the mirror source LU and the LU 262 that is the mirror destination LU can be shortened, and the amount of update positions recorded in the non-mirror update position management table 222 can be reduced. Can do. Therefore, when mirror resynchronization is performed, the amount of copy of the updated original data from the mirror source LU to the mirror destination LU can be reduced, and the mirror resynchronization time during which the data access performance from the computer 100 decreases. There is an effect that can be shortened.
[0041]
When the amount of snapshot data is the same, the duplexing stop time is inversely proportional to the transfer rate when the snapshot is sent from the mirror destination LU and taken into the receiver side. Since the mirror resynchronization time is proportional to the amount of data updated during duplexing stop, assuming that update access occurs the same number of times per unit time, the mirror resynchronization time is proportional to the duplexing stop time. Therefore, the mirror resynchronization time is inversely proportional to the transfer rate when the snapshot is sent from the mirror destination LU and taken into the receiver side.
[0042]
For example, assuming that the transfer capacity of the disk controller 250 in this embodiment has a sufficient margin, if the read / write performances of the LUs 261 to 263 are both 80 megabytes / second, the mirror destination LU is 80 megabytes / second. Snapshots can be copied from a temporary LU to a temporary LU. Therefore, in this embodiment, the transfer rate when a snapshot is sent from the mirror destination LU and taken into the receiver side is 80 megabytes / second. Here, the bytes / second is the number of bytes of data that can be transferred per second.
[0043]
On the other hand, when a backup is taken to a tape by a conventional method, a snapshot is read from the mirror destination LU, transferred to a computer, and further written to the tape from there. The overall transfer performance is the lowest value among the read performance of the mirror destination LU, the transfer performance from the disk array to the computer, the internal transfer performance of the computer, the transfer performance from the computer to the tape, and the write performance of the tape. Similarly, the read performance of the mirror destination LU is 80 megabytes / second, but the tape write performance is low from the viewpoint of winding performance. For example, if the performance is 40 megabytes / second, the overall transfer performance is 40 megabytes / second. Therefore, in the conventional method, the transfer rate when the snapshot is sent from the mirror destination LU and taken into the receiver side is 40 megabytes / second. In addition, the transfer performance of other parts may be low.
[0044]
Therefore, in a trial calculation in which both the read / write performance of the LUs 261 to 263 is 80 megabytes / second and the write performance of the tape is 40 megabytes / second, this embodiment sends a snapshot from the mirror destination LU to the conventional method. The transfer speed when taking in the receiver side is doubled. Since the mirror resynchronization time is inversely proportional to the transfer speed when the snapshot is sent from the mirror destination LU and taken into the receiver side, this embodiment halves the mirror resynchronization time compared to the conventional method. be able to.
[0045]
Further, according to the present embodiment, by providing the LU 263, which is a temporary LU, as a temporary temporary area for storing a snapshot, there is no need to instruct deletion of the snapshot after using the snapshot. Can simplify the program to implement. Therefore, since the program development period can be shortened, there is an effect that an inexpensive system can be configured.
[0046]
In the present invention, the SCSI bus 300 is used as an interface for connecting the computer 100 and the disk array 200, but another interface such as Fiber Channel may be used.
[0047]
If the original data of the LU 261 at the time of snapshot acquisition is to be restored, the snapshot is stored in the LU 263, which is a temporary LU, so the LU 263 may be switched to the mirror source LU.
[0048]
In addition, when the snapshot is acquired, the issue of the ModeSelect command instructing the start of temporary copy in step 2004 of FIG. 4 can be omitted. In this case, steps 3005 to 3008 may be performed after the snapshot management program 221 ends step 3003. If the status resulting from the execution of steps 3005 to 3008 results in an error, the status for any command issued from the computer 100 is set to Check Condition, and in response to the RequestSense command issued by the computer 100 in response thereto. Sense data that conveys an error may be transmitted.
[0049]
[Second Embodiment]
The second embodiment of the present invention is similar to the first embodiment in the snapshot management method based on data duplication in which the resynchronization time is reduced by shortening the time during which the duplication is stopped. This is to reduce the copy amount of the original data and shorten the mirror resynchronization time in which the data access performance from the database program is lowered.
[0050]
Further, as in the first embodiment, the backup program is simplified by omitting the snapshot deletion instruction after using the snapshot.
[0051]
The difference from the first embodiment is that when a snapshot is saved in a temporary LU, the difference from the snapshot saved in the previous temporary LU is copied to the temporary LU, not the entire mirror destination LU. is there.
[0052]
In the present invention, a backup is taken as an example of using a snapshot, but it can also be used for other purposes such as OLAP (OnLine Analytical Processing) and system testing.
[0053]
(1) Description of configuration
The system configuration of the second embodiment of the present invention will be described with reference to FIG. For the sake of simplicity, only differences from the first embodiment will be described.
[0054]
In FIG. 6, an LU 263 is a temporary LU that stores a temporary snapshot as in the first embodiment, and at the same time is a temporary LU that stores a previous snapshot.
[0055]
In addition to the first embodiment, the snapshot management program 221 of the disk array 200 includes a constant update monitoring subprogram 237 that detects updates to the mirror source LU from the snapshot acquisition time to the next snapshot acquisition time, and the update thereof. It has a constantly updated position management subprogram 238 that records positions in a constantly updated position management table 224 to be described later.
[0056]
The temporary copy subprogram 233 acquires a snapshot in addition to the function of the first embodiment in which original data is temporarily copied (temporary copy) from a mirror destination LU to a temporary LU when a snapshot is acquired. A function of copying the difference from the previous snapshot from the mirror destination LU to the temporary LU in which the previous snapshot is stored. The temporary copy subprogram 233 has a function of recording the position where the copy is completed in the constantly updated position management table 224 determined at the time of snapshot acquisition. The temporary update position management table 224 determined at the time of snapshot acquisition at the time of temporary copy replaces the copy position management table 223 of the first embodiment, and the computer 100 snapshots the LU 261 in the disk array 200. , The snapshot management program 221 refers to the constantly updated location management table 224 determined at the time of snapshot acquisition instead of the copy location management table 223 of the first embodiment.
[0057]
The constantly updated position management table 224 records the update position of the mirror source LU updated from the snapshot acquisition time to the next snapshot acquisition time, and after the recording of the update status is stopped and confirmed. In addition, since it is necessary to continuously monitor the update position in preparation for the next snapshot acquisition, at least two update position management tables 224 are provided for each mirror source LU. The constantly updated position management table 224 is a bitmap as shown in FIG. 7 and includes all LBA set numbers and update states in the mirror source LU. The definition of the LBA set number and the update state is the same as that in the non-mirror update position management table 222. The initial setting value of the update state is 0 for the first and second snapshots after the first snapshot acquisition. In the example of FIG. 7, only the area of LBA set number 1 is updated between the snapshot acquisition time and the next snapshot acquisition time. Note that the designated value of the update state in the constantly updated location management table 224 is 0 when the data matches between the LU 261 that is the mirror source LU and the LU 263 of the temporary LU that stores the previous snapshot. The case where it is not done can be rephrased as 1.
[0058]
(2) Acquisition of snapshot
In the second embodiment, unlike the first embodiment, when a snapshot is acquired, a new snapshot is obtained by copying the difference data after the snapshot acquisition to the temporary LU that saved the previous snapshot. Is stored in the temporary LU. In the first snapshot acquisition, there is no temporary LU storing the previous snapshot, so the procedure is the same as in the first embodiment. However, since the differential copy is performed at the time of the next snapshot saving, the snapshot management program 221 performs a constant update monitoring subprogram for creating the constant update position management table 224 in the step following step 3001 in FIG. 237 and the constantly updated location management subprogram 238 are activated. Thereafter, when there is a data write request from the database program 126, 1 is set in the update state of the LBA set including the updated LBA in the constantly updated location management table 224, and the fact that there has been an update is recorded.
[0059]
Next, a procedure for acquiring the snapshot after the second time and saving the snapshot to the temporary LU will be described.
[0060]
Also in the second and subsequent snapshot acquisition, the constantly updated position management table 224 records the update status from the snapshot acquisition to the next snapshot acquisition. In the step following step 3001 in FIG. 4, the snapshot management program 221 determines the constantly updated position management table 224 that records the updates from the previous snapshot to the current snapshot, and from the current snapshot to the next snapshot. Recording of the constantly updated position management table 224 until the shot is started. Thereafter, the snapshot management program 221 determines the constantly updated position management table 224 in the next step after step 3001 in FIG. 4 and starts recording the next constantly updated position management table 224.
[0061]
In addition, the previous snapshot is still stored in the temporary LU LU 263.
[0062]
At the time of temporary copy, the snapshot management program 221 refers to the constantly updated position management table 224 determined at the time of snapshot acquisition by the temporary copy subprogram 233, and changes from the LU 262 that is the mirror destination LU to the LU 263 that is the temporary LU. Make a differential copy of the previous snapshot. Other operations are the same as those in the first embodiment.
[0063]
Here, the temporary copy subprogram operation at the time of the temporary copy for copying the difference will be described with reference to the flowchart of FIG. First, the snapshot management program 221 checks whether there is 1 in the update state as an update record in the constantly updated location management table 224 (step 1201). If there is no update record 1, the process is completed (step 1202). Otherwise, the data at the corresponding recording position is copied from the mirror destination LU 262 to the temporary LU 263 (step 1203). For data copying, the READ command is issued to the disk 252 including the LU 262 to read the specified LBA data, the WRITE command is issued to the disk 253 including the LU 263, and the data read to the same LBA as the LBA specified to the LU 262 is read. Implement by writing. The COPY command may be used to copy the data. Finally, 0 is set in the corresponding update record in the constantly updated position management table 224 to delete the update record (step 1204), and the process returns to step 1201.
[0064]
(3) Computer operation when reading and writing data and reading snapshots
The operation of the database program 126 when the computer 100 accesses the data of the LU 261 in the disk array 200 and the operation of the backup program 127 when the computer 100 reads the snapshot of the LU 261 in the disk array 200 are as follows. This is the same as the first embodiment.
[0065]
(4) Disk array operation when reading and writing data and reading snapshots
First, the operation of the snapshot management program 221 when the computer 100 accesses the data of the LU 261 in the disk array 200 will be described.
[0066]
The operation of the snapshot management program 221 when the computer 100 reads data from the LU 261 is the same as that in the first embodiment.
[0067]
When the computer 100 writes data to the LU 261 and updates the stored contents, the snapshot management program 221 receives a WRITE command and data for the LU 261. Next, if the LU mirror subprogram 231 is valid, data is written to the LU 261 and the mirror destination LU 262, and if invalid, data is written to the LU 261. Next, the update state of the LBA set including the updated LBA is set to 1 in the constantly updated position management table 224 of the mirror source LU that is recording the update. Next, if the non-mirror time update monitoring subprogram 234 and the non-mirror time update position management subprogram 235 are valid, the update state of the LBA set including the LBA updated to the non-mirror time update position management table 222 of the LU 261 Set to 1 and do nothing if disabled. Finally, the status is transmitted to the computer 100.
[0068]
Next, the operation of the snapshot management program 221 when the computer 100 reads a snapshot of the LU 261 in the disk array 200 will be described.
[0069]
When the computer 100 reads a snapshot of the LU 261, the snapshot management program 221 receives a READ command for the LU 263 that is a temporary LU of the LU 261. Next, the snapshot management program 221 refers to the constantly updated location management table 224 that is determined at the time of snapshot acquisition and is used instead of the copy location management table 223 in the first embodiment at the time of temporary copy, The update state of the LBA set including the LBA specified in (1) is checked. When the update state is 0, that is, when a snapshot of the LU 261 is stored in the LU 263 that is a temporary LU, data is read from the LU 263. When the copy state is 1, that is, when the snapshot of the LU 261 is not stored in the LU 263 that is a temporary LU, data is read from the LU 262 that is a mirror destination LU. Finally, the read data and status are transmitted to the computer 100. When the snapshot data cannot be transmitted, only the error status is transmitted to the disk array 200.
[0070]
(5) Effect
In the second embodiment, as in the first embodiment, by providing an LU 263 that is a temporary LU as a temporary temporary area for storing a snapshot, an LU 261 that is a mirror source LU and a mirror destination LU. It is possible to reduce the duplication stop time of the LU 262, and the amount of update positions recorded in the non-mirror update position management table 222 can be reduced. Furthermore, in the second embodiment, since the previous snapshot is stored in the temporary LU and only the difference from the previous snapshot is copied during the temporary copy, the duplication stop time of the LU 261 and LU 262 can be further shortened. it can. Therefore, when mirror resynchronization is performed, the amount of copy of the updated original data from the mirror source LU to the mirror destination LU can be reduced, and the mirror resynchronization time during which the data access performance from the computer 100 decreases. There is an effect that can be shortened.
[0071]
Further, in the second embodiment, as in the first embodiment, by providing the LU 263, which is a temporary LU, as a temporary temporary area for storing a snapshot, the snapshot is deleted after using the snapshot. Therefore, it is possible to simplify the program for performing backup. Therefore, since the program development period can be shortened, there is an effect that an inexpensive system can be configured.
[0072]
Further, as a copy method at the time of temporary copy, a copy method selection subprogram capable of selecting the method of copying the entire LU 262 in the first embodiment and the method of copying only the difference between the LU 262 and the LU 263 of the second embodiment Adding to the snapshot management program 221 is also conceivable. This is based on the assumption that when the update from the previous snapshot is performed in almost all areas in the LU 261, copying the entire LU 262 continuously from the beginning of the LBA set may shorten the copy time. It is a thing. Thus, the user can select a temporary copy method according to the amount of update data from the previous snapshot, and the temporary copy can be efficiently performed. Therefore, since the duplication stop time of the LU 261 and the LU 262 can be shortened, the amount of copying the updated original data from the mirror source LU to the mirror destination LU can be reduced when performing mirror resynchronization. The mirror resynchronization time during which the data access performance from the computer 100 is reduced can be shortened.
[0073]
In the present invention, the SCSI bus 300 is used as an interface for connecting the computer 100 and the disk array 200, but another interface such as Fiber Channel may be used.
[0074]
If the original data of the LU 261 at the time of snapshot acquisition is to be restored, the snapshot is stored in the LU 263, which is a temporary LU, so the LU 263 may be switched to the mirror source LU.
[0075]
In addition, when the snapshot is acquired, the issue of the ModeSelect command instructing the start of temporary copy in step 2004 of FIG. 4 can be omitted. In this case, steps 3005 to 3008 may be performed after the snapshot management program 221 ends step 3003. If the status resulting from the execution of steps 3005 to 3008 results in an error, the status for any command issued from the computer 100 is set to Check Condition, and in response to the RequestSense command issued by the computer 100 in response thereto. Sense data that conveys an error may be transmitted.
[0076]
【The invention's effect】
As described above, according to the present invention, in the snapshot management method for duplicating data into two storage areas, stopping the duplication at the time of snapshot acquisition and providing one storage area as a snapshot, By providing a temporary LU consisting of a high-speed disk in the disk array as a temporary temporary area for saving, the time during which duplication is stopped for snapshot acquisition can be shortened. Therefore, when mirror resynchronization is performed, the amount of copied original data copied to the mirror destination LU can be reduced, and the mirror resynchronization time during which data access performance from the database program is reduced can be shortened. effective.
[0077]
Further, according to the present embodiment, by providing a temporary LU as a temporary temporary area for saving a snapshot, it is not necessary to instruct deletion of the snapshot after using the snapshot. The program can be simplified. Therefore, since the program development period can be shortened, an inexpensive system can be configured.
There is an effect.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram according to a first embodiment.
FIG. 2 is an explanatory diagram of a non-mirrored update position management table in the first embodiment.
FIG. 3 is an explanatory diagram of a copy position management table according to the first embodiment.
FIG. 4 is a snapshot acquisition flow in the first embodiment.
FIG. 5 is an operation flow of a mirror resynchronization subprogram in the first embodiment.
FIG. 6 is a system configuration diagram according to the second embodiment.
FIG. 7 is an explanatory diagram of a constantly updated position management table according to the second embodiment.
FIG. 8 is an operation flow of a temporary copy subprogram in the second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 ... Computer, 126 ... Database program, 127 ... Backup program, 200 ... Disk array, 221 ... Snapshot management program, 222 ... Non-mirror update position management table.

Claims (5)

A processor that processes requests from the host device;
A memory connected to the processor for storing information;
A first logical unit to be accessed from the host device;
A second logical unit in which data of the first logical unit is stored;
A third logical unit in which data is temporarily stored;
Have
The memory includes a first update location management table storing updated locations of data written to the first logical unit;
A second updated location management table storing updated locations of data written from the second logical unit to the third logical unit;
Third update location management in which an updated location of data written in the first logical unit is stored between a request to obtain a snapshot from the host device and a request to obtain the next snapshot A table, and
The processor writes the write data transmitted from the host device to the first logical unit, and writes the write data to the second logical unit,
When receiving a first request for acquiring a snapshot from the higher-level device, the processor updates the location updated in the first logical unit with the first update location management table and the third update location management. Recording in a table and stopping writing data to the second logical unit;
The processor writes the data of the second logical unit to the third logical unit and records the written position in the second update position management table,
After the writing of data to the third logical unit is completed, the processor is updated from the first logical unit to the second logical unit based on the first update location management table. Write data,
Further, when writing a data from the second logical unit to the third logical unit when a second request for acquiring a snapshot is received from the host device, the processor updates the second update management table. A storage system for selecting whether to write data using the data or to write data based on the third update management table. The storage system of claim 1, wherein
When the host device reads snapshot data corresponding to the first request, the processor uses the second update location management table or the third update location management table to determine whether the second logical unit or the second A storage system for reading the snapshot data from three logical units. The storage system of claim 1, wherein
A storage system having a disk controller connected to the processor and the first to third logical units and accessing the first to third logical units according to instructions from the processor. The storage system of claim 3.
A disk access program that instructs the disk controller to access the first to third logical units in response to a request from the computer;
An LU mirror subprogram in which the processor writes data updated in the first logical unit to the second logical unit;
A snapshot management program in which the processor writes data from the second logical unit to the third logical unit;
A non-mirrored update monitoring program for detecting an update to the first logical unit when the processor stops writing updated data from the first logical unit to the second logical unit;
A non-mirrored update location management program for storing the updated location for the first logical unit in the memory;
A mirror resynchronization program in which the processor synchronizes again from the first logical unit to the second logical unit;
A storage system having the memory. The storage system of claim 1, wherein
The memory has a plurality of the third update management tables for the first logical unit,
When a third request for acquiring a snapshot is received from the host device,
The storage system, after confirming the third update management table, creates a new third update management table for recording the position of the update from the third request.

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