Methods and structure for improved migration of raid logical volumes

1 . A method of migrating a volume of a RAID storage subsystem from a first RAID level to a second RAID level, wherein said volume comprises a plurality of disk drives (N) and wherein said volume comprises a plurality of stripes and wherein each stripe comprises a corresponding plurality of data blocks and at least a first block of corresponding redundancy information, the method comprising the steps of:

reconfiguring each stripe of said plurality of stripes such that said each stripe comprises said corresponding plurality of data blocks and a reduced number of blocks of corresponding redundancy information; and

reducing the number of said plurality of disk drives from N,

whereby the volume is migrated from said first RAID level to said second RAID level.

2 . The method of claim 1

wherein said first RAID level is level 6 such that said each stripe includes a first block of corresponding redundancy information and a second block of corresponding redundancy information, and

wherein said second RAID level is level 5, and

wherein the step of reconfiguring comprises reconfiguring said plurality of stripes such that said each stripe comprises said corresponding plurality of data blocks and said first block of corresponding redundancy information and wherein said each stripe is devoid of said second block of redundancy information; and

wherein the step of reducing comprises reducing the number of said plurality of disk drives from N to N−1.

3 . The method of claim 1

wherein said first RAID level is level 6 and wherein said second RAID level is level 0; and

wherein the step of reconfiguring comprises reconfiguring said plurality of stripes such that said each stripe contains said corresponding plurality of data blocks and is devoid of all redundancy information; and

wherein the step of reducing comprises reducing the number of said plurality of disk drives from N to N−2.

4 . The method of claim 1

wherein said first RAID level is level 5 and wherein said second RAID level is level 0; and

wherein the step of reconfiguring comprises reconfiguring said plurality of stripes such that each stripe contains said plurality of data blocks and is devoid of redundancy information; and

wherein the step of reducing comprises reducing said plurality of disk drives is from N toN−1.

5 . The method of claim 1

wherein the step of reducing results in one or more of said plurality of disk drives of the volume being unused disk drives; and

the step of reducing includes a step of releasing said unused disk drives.

6 . The method of claim 1

wherein the step of reconfiguring is devoid of a need to move any blocks for a subset of said plurality of stripes during reconfiguration.

7 . The method of claim 1

wherein each stripe of said plurality stripes is associated with a stripe identifier sequentially assigned from a sequence starting at 1 and incremented by 1; and

wherein the step of reconfiguring is devoid of a need to move any blocks during reconfiguration when said stripe identifier is equal to a modulo finction of N.

8 . The method of claim 7

wherein the step of reconfiguring is devoid of a need to move any blocks during reconfiguration when the stripe identifier is equal to a multiple of N.

9 . The method of claim 1

wherein the step of reconfiguring needs to move at most one block for each stripe of said plurality of stripes during reconfiguration.

10 . A RAID storage subsystem comprising:

a plurality of disk drives;

a volume comprising a number of assigned disk drives (N) from said plurality of disk drives wherein said volume comprises a plurality of stripes wherein each stripe of said plurality of stripes comprises a plurality of data blocks and at least one block of redundancy information; and

a storage controller coupled to said plurality of disk drives to process I/O requests received from said host system; and

wherein the storage controller further comprises:

a migration manager adapted to migrate the volume from a first RAID level to a second RAID level by reconfiguring said each stripe to contain said plurality of data blocks and a reduced number of blocks of redundancy information; and

a drive elimination manager operable responsive to said migration manager to reduce said number of assigned disk drives of the volume below N.

11 . The system of claim 10 wherein said drive elimination is adapted to eliminate one or more of said assigned disk drives to generate one or more unused disk drives and wherein said drive elimination manager is further adapted to release said unused disk drives for use by other volumes.

12 . The system of claim 10 wherein said first RAID level is RAID level 6 and wherein said second RAID level is RAID level 5 and

wherein said drive elimination is adapted to eliminate one of said assigned disk drives to generate one unused disk drive and wherein said drive elimination manager is further adapted to release said unused disk drive for use by other volumes.

13 . The system of claim 10 wherein said first RAID level is RAID level 5 and wherein said second RAID level is RAID level 0 and

wherein said drive elimination is adapted to eliminate one of said assigned disk drives to generate one unused disk drive and wherein said drive elimination manager is further adapted to release said unused disk drive for use by other volumes.

14 . The system of claim 10 wherein said first RAID level is RAID level 6 and wherein said second RAID level is RAID level 0 and

wherein said drive elimination is adapted to eliminate two of said assigned disk drives to generate two unused disk drives and wherein said drive elimination manager is further adapted to release said unused disk drives for use by other volumes.

15 . The system of claim 10 wherein said reconfiguration manager is adapted to operate devoid of a need to move any of the plurality of data blocks for multiple of the plurality of stripes of the volume.

16 . A method operable in a storage subsystem for migrating a RAID logical volume in the subsystem from a first RAID level to a second RAID level wherein the logical volume configured in the first RAID level is striped over a plurality of disk drives and wherein each stripe has a plurality of data blocks and has wherein each stripe has at least one redundancy block, the method comprising the steps of:

selecting a disk drive of the plurality of disk drive to be logically removed from the logical volume leaving a remaining set of disk drive in the logical volume; and

reconfiguring each stripe of the logical volume from the first RAID level to the second RAID level by eliminating a redundancy block associated with the first RAID level in said each stripe and by reorganizing remaining blocks of said each stripe required for the second RAID level to reside exclusively on the remaining set disk drives.

17 . The method of claim 16 further comprising:

freeing the selected disk drive for use in other logical volumes following completion of the step of reconfiguring.

18 . The method of claim 16 wherein the first RAID level is level 6 and wherein the second RAID level is level 5 and wherein the step of reconfiguring further comprises:

eliminating a second redundancy block from said each stripe and reorganizing the data blocks and first redundancy block remaining in said each stripe to reside only on the remaining set of disk drives.

19 . The method of claim 16 wherein the first RAID level is level 5 and wherein the second RAID level is level 0 and wherein the step of reconfiguring further comprises:

eliminating a redundancy block from said each stripe and reorganizing the data blocks remaining in said each stripe to reside only on the remaining set of disk drives.

20 . The method of claim 16 wherein the first RAID level is level 6 and wherein the second RAID level is level 0 and wherein the step of reconfiguring further comprises:

eliminating a first and second redundancy block from said each stripe and reorganizing the data blocks remaining in said each stripe to reside only on the remaining set of disk drives.