Snapback-free logical drive duplication
There is provided a method of duplicating a logical drive. The method includes sequentially copying data from a source logical drive to a destination logical drive and determining whether a write request is received to a data area on the source logical drive which has not yet been copied to the destination logical drive. If a write request is detected, the data at the write-requested data area is copied to the destination logical drive prior to executing the write request. By providing such a method, the destination logical drive can be used as the change-data store while in the process of the duplication operation, removing the need for a snapshot logical drive in the duplication process. This results in improvements in duplication speed and reduces drive wear due to the reduced number of data reads/writes.
1. A method of creating an identical copy of a source logical drive on a destination logical drive, the destination logical drive being directly accessible for read/write operations, the method comprising:
starting a duplication operation;
sequentially copying data from the source logical drive to the destination logical drive; and
determining whether, subsequent to starting said duplication operation, a write request is received to a data area on the source logical drive which has not yet been copied to said destination logical drive by said sequential copy process and, if such a write request is received during said sequential copy process:
copying, independently of said sequential copy process, the data at said write-requested data area to the destination logical drive;
executing said write request; and
ignoring the data at said write-requested data area during said sequential copying process.
2. A method according to claim 1 , wherein if said write request is received, the method further comprises the step of storing information regarding said write-requested data area in a data file or memory.
3. A method according to claim 2 , wherein said data file is a bitmap.
4. A method according to claim 2 , wherein said step of ignoring said data at said write-requested data area comprises determining, from said data file or memory, the data area to be ignored during said sequential copying.
5. A method according to claim 1 , wherein said data is arranged in a plurality of logical blocks.
6. A method according to claim 5 , wherein the step of sequential copying starts with the first or last logical block in a group of logical blocks.
7. A method according to claim 6 , wherein the step of sequential copying starts with the first or last logical block on the source drive.
8. Apparatus for creating an identical copy of a source logical drive on a destination logical drive, the destination logical drive being directly accessible for read/write operations, the apparatus comprising:
a controller comprising a physical processor, the controller operable to start a duplication operation and to copy sequentially data from the source logical drive to the destination logical drive; and
an access manager operable to determine whether, subsequent to starting said duplication operation, a write request is received to a data area on the source logical drive which has not yet been copied to said destination logical drive by said sequential copy process and, if such a write request is received during said sequential copy process, the controller is further operable to:
copy, independently of said sequential copy process, the data at said write-requested data area to the destination logical drive;
execute said write request; and
ignore the data at said write-requested data area during said sequential copying process.
9. Apparatus according to claim 8 , wherein if said write request is received, the apparatus is operable to store information regarding said write-requested data area in a data file or a memory.
10. Apparatus according to claim 9 , wherein said data file is a bitmap.
11. Apparatus according to claim 9 , further operable to determine, from said data file or memory, the data area to be ignored during said sequential copying.
12. Apparatus according to claim 8 , wherein said data is arranged in a plurality of logical blocks.
13. Apparatus according to claim 12 , wherein the apparatus is further operable to start said sequential copying with the first or last logical block in a group of logical blocks.
14. Apparatus according to claim 13 , wherein the apparatus is further operable to start said sequential copying with the first or last logical block on the source drive.
15. Apparatus according to claim 8 in the form of a controller.
16. Apparatus according to claim 15 in the form of a RAID controller.
17. Apparatus according to claim 16 , wherein the RAID controller comprises firmware, software or a combination of both on a host.
18. Apparatus according to claim 16 , wherein the RAID controller comprises firmware, software or a combination of both in an off-host controller.
19. A data storage resource comprising at least one physical drive and a controller according to claim 15 .
20. A non-transitory computer usable storage medium having a computer program product executable by a programmable processing apparatus, comprising one or more software portions for performing the steps of claim 1 .