Technique for increasing the number of persistent consistency point images in a file system
An on-disk storage arrangement increases the number of persistent consistency point images (PCPIs) that may be maintained for a volume of a storage system. The on-disk storage arrangement comprises a novel volume information (volinfo) block representing a root of the volume; the volinfo block is stored at predefined locations on disk and comprises various system wide configuration data. The volinfo block further comprises a data structure configured to provide a level of indirection that increases the number of PCPIs maintainable by a file system executing on the storage system. To that end, the data structure may be organized as an array of pointers, wherein each pointer references a block containing a snapshot root, thereby enabling efficient access to each PCPI maintained by the file system.
1. A method for increasing a number of persistent consistency point images (PCPIs) maintained for a volume of a storage system, the method comprising the steps of:
providing a file system information (fsinfo) block associated with an active file system executing on the storage system;
providing one or more PCPI fsinfo blocks, each PCPI fsinfo block associated with a PCPI; and
providing a volume information (volinfo) block at a predetermined location on disk of the storage system, the volinfo block comprising a plurality of pointers configured to reference the fsinfo and PCPI fsinfo blocks.
2. The method of claim 1 wherein the pointers comprise volume block numbers.
3. The method of claim 1 further comprising the steps of:
organizing the pointers as a table having a plurality of entries, each entry storing a pointer; and
indexing the entries of the table by PCPI identifier (ID).
4. The method of claim 3 further comprising the step of associating the active file system with a predefined PCPI ID.
5. The method of claim 1 further comprising the steps of:
organizing the pointers as an array indexed by PCPI identifier (ID); and
associating the active file system with a predefined PCPI ID.
6. The method of claim 5 wherein the predefined PCPI ID is zero.
7. The method of claim 1 wherein the fsinfo block comprises a pointer configured to reference an inode file associated with the active file system.
8. The method of claim 1 wherein each PCPI fsinfo block comprises a pointer configured to reference an inode file associated with a PCPI.
9. The method of claim 1 wherein the predetermined location comprises a first and second volume block number.
10. The method of claim 1 wherein the volinfo block further comprises fields for PCPIs that do not have associated PCPI fsinfo blocks referenced by the volinfo block.
11. A system adapted to maintain an increased number of persistent consistency point images (PCPI) for a volume of a storage system, the system comprising:
at least one storage device adapted to store a volume information (volinfo) block at a predefined location, the storage device further adapted to store a plurality of file system information (fsinfo) blocks referenced by the volinfo block.
12. The system of claim 11 wherein the storage device is a disk.
13. The system of claim 11 wherein the predefined location comprises a first and second volume block number.
14. The system of claim 11 wherein the fsinfo blocks comprise a first fsinfo block associated with an active file system and having a pointer configured to reference an inode file associated with the active file system.
15. The system of claim 11 wherein the volinfo block comprises an array of pointers configured to reference the fsinfo blocks.
16. The system of claim 15 wherein the array of pointers is indexed by a PCPI identifier (ID) and wherein an active file system is associated with a predefined PCPI ID.
17. The storage system of claim 15 wherein each pointer comprises a volume block number.
18. Apparatus for increasing a number of persistent consistency point images (PCPIs) maintained for a volume of a storage system, the apparatus comprising:
means for providing a file system information (fsinfo) block associated with an active file system executing on the storage system;
means for providing one or more PCPI fsinfo blocks, each PCPI fsinfo block associated with a PCPI; and
means for providing a volume information (volinfo) block at a predetermined location on disk of the storage system, the volinfo block comprising a plurality of pointers configured to reference the fsinfo and PCPI fsinfo blocks.
19. A computer readable medium, including program instructions executing on a storage system, for increasing a number of persistent consistency point images (PCPIs) maintained for a volume of the storage system, the computer readable medium including program instructions for:
providing a file system information (fsinfo) block associated with an active file system executing on the storage system;
providing one or more PCPI fsinfo blocks, each PCPI fsinfo block associated with a PCPI; and
providing a volume information (volinfo) block at a predetermined location on disk of the storage system, the volinfo block comprising a plurality of pointers configured to reference the fsinfo and PCPI fsinfo blocks.
20. The computer readable medium of claim 19 further comprising program instructions for:
organizing the pointers as an array indexed by PCPI identifier (ID); and
associating an active file system with a predefined PCPI ID.