Hello,
Thought I'd share this 'trick' (if using the documented functionality can be
called that :).
I needed to upgrade my 3-disk RAID5 to a 5-disk RAID6. Problem is, due to a
lack of free space I needed to do that in stages, i.e. add one drive, gain
additional space in the array, move some data over, then add another drive.
The usual way of doing this perhaps would be to first reshape to a 4-disk
RAID5, and only after that to a 5-disk RAID6.
But I wanted to have this done in just one reshape. So I got the idea to
reshape from a 3-disk RAID5 right to a degraded 5-disk RAID6 (with 4 drives
active and one missing).
On my RAID5 with 3 "active" drives and 1 newly-added "spare" drive I executed:
mdadm --grow --level=6 --raid-devices=5 /dev/md0
And indeed, this worked exactly as intended:
/dev/md0:
Version : 1.2
Creation Time : Wed Jun 9 12:14:49 2010
Raid Level : raid6
Array Size : 3887004672 (3706.94 GiB 3980.29 GB)
Used Dev Size : 1943502336 (1853.47 GiB 1990.15 GB)
Raid Devices : 5
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Fri Apr 8 11:52:03 2011
State : clean, degraded, recovering
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric-6
Chunk Size : 64K
Reshape Status : 0% complete
Delta Devices : 1, (4->5)
New Layout : left-symmetric
Name : natsu:0 (local to host natsu)
UUID : 7f0c87dd:bcd14e11:7624e659:a7701e85
Events : 35389
Number Major Minor RaidDevice State
0 8 35 0 active sync /dev/sdc3
1 8 67 1 active sync /dev/sde3
3 8 51 2 active sync /dev/sdd3
4 8 99 3 spare rebuilding /dev/sdg3
4 0 0 4 removed
--
With respect,
Roman
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