Hello,
I'm using the new mdadm-3.1.1 and kernel 2.6.32 on a 13x 1TB RAID6
array and need to reduce the number of active devices in order to
eventually decommission this array.
I'm currently unable to do this however, please see below:
array:~ # uname -a
Linux array 2.6.32-41-default #1 SMP 2009-12-11 11:05:24 -0500 x86_64
x86_64 x86_64 GNU/Linux
array:~ # mdadm -V
mdadm - v3.1.1 - 19th November 2009
array:~ # mdadm -D /dev/md0
/dev/md0:
Version : 0.90
Creation Time : Fri Apr 4 21:17:09 2008
Raid Level : raid6
Array Size : 10744387456 (10246.65 GiB 11002.25 GB)
Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
Raid Devices : 13
Total Devices : 13
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Wed Jan 13 13:43:05 2010
State : clean
Active Devices : 13
Working Devices : 13
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
UUID : 251f6c00:b15f5541:4eb0bc47:eeccb517
Events : 0.6050151
Number Major Minor RaidDevice State
0 8 0 0 active sync /dev/sda
1 8 16 1 active sync /dev/sdb
2 8 32 2 active sync /dev/sdc
3 8 224 3 active sync /dev/sdo
4 8 64 4 active sync /dev/sde
5 8 80 5 active sync /dev/sdf
6 8 96 6 active sync /dev/sdg
7 8 112 7 active sync /dev/sdh
8 8 144 8 active sync /dev/sdj
9 8 160 9 active sync /dev/sdk
10 8 176 10 active sync /dev/sdl
11 8 192 11 active sync /dev/sdm
12 8 208 12 active sync /dev/sdn
array:~ #
## Reduce array size by 1x member disk in order to verify data will
remain accessible after reducing array. There is a reiser filesystem
directly on this MD device, already resized to ~300GB below the
reduced array size:
array:~ # mdadm -G /dev/md0 --array-size 9767624960 (short size option
-Z segfaults as already discussed)
## Verify new array size is now @ sum of 10x member disks:
array:~ # mdadm -D /dev/md0
/dev/md0:
Version : 0.90
Creation Time : Fri Apr 4 21:17:09 2008
Raid Level : raid6
Array Size : 9767624960 (9315.13 GiB 10002.05 GB)
Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
Raid Devices : 13
Total Devices : 13
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Wed Jan 13 15:06:33 2010
State : active
Active Devices : 13
Working Devices : 13
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
UUID : 251f6c00:b15f5541:4eb0bc47:eeccb517
Events : 0.6050154
Number Major Minor RaidDevice State
0 8 0 0 active sync /dev/sda
1 8 16 1 active sync /dev/sdb
2 8 32 2 active sync /dev/sdc
3 8 224 3 active sync /dev/sdo
4 8 64 4 active sync /dev/sde
5 8 80 5 active sync /dev/sdf
6 8 96 6 active sync /dev/sdg
7 8 112 7 active sync /dev/sdh
8 8 144 8 active sync /dev/sdj
9 8 160 9 active sync /dev/sdk
10 8 176 10 active sync /dev/sdl
11 8 192 11 active sync /dev/sdm
12 8 208 12 active sync /dev/sdn
array:~ #
## Mount / verify file checksums etc - all OK
## Attempt to reduce number of active devices in array by 1x:
array:~ # mdadm -G /dev/md0 -n 12 --backup-file /tmp/md0-backup
mdadm: this change will reduce the size of the array.
use --grow --array-size first to truncate array.
e.g. mdadm --grow /dev/md0 --array-size 1177690368
## The suggested value of '--array-size' here doesn't make sense; plus
when trying to reduce to a different number of active devices (e.g.
11x, invalid), this number changes:
array:~ # mdadm -G /dev/md0 -n 11 --backup-file /tmp/md0-backup
mdadm: this change will reduce the size of the array.
use --grow --array-size first to truncate array.
e.g. mdadm --grow /dev/md0 --array-size 200927872
## Attempting to reduce to 10x active devices (invalid) gives a
different result again:
array:~ # mdadm -G /dev/md0 -n 10 --backup-file /tmp/md0-backup
mdadm: Need to backup 5632K of critical section..
array:~ #
## However (almost) nothing happens - the backup-file does get written
however there is no rebuild initiated and the array stays the same
size.
Testing this in a VM with 128MB loopback devices works as expected and
the filesystem / data survives.
Any ideas ? I saw there was mention recently of a patch to mdadm-3.1.1
which resolves a 32-bit number affecting growing of a RAID6, could
this also be the issue here ?
Thanks in advance,
Brett.
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