On Wed, 12 Sep 2012 10:59:56 +0600 Roman Mamedov <rm@xxxxxxxxxx> wrote:
> Hello,
>
> # mdadm --detail /dev/md1
> /dev/md1:
> Version : 1.2
> Creation Time : Fri May 27 09:50:54 2011
> Raid Level : raid1
> Array Size : 488372863 (465.75 GiB 500.09 GB)
> Used Dev Size : 488372863 (465.75 GiB 500.09 GB)
> Raid Devices : 2
> Total Devices : 3
> Persistence : Superblock is persistent
>
> Intent Bitmap : Internal
>
> Update Time : Wed Sep 12 10:54:33 2012
> State : active
> Active Devices : 2
> Working Devices : 3
> Failed Devices : 0
> Spare Devices : 1
>
> Name : avdeb:1 (local to host avdeb)
> UUID : e29a222d:e6245302:5ff3f834:ad471a01
> Events : 26
>
> Number Major Minor RaidDevice State
> 0 8 82 0 active sync /dev/sdf2
> 1 8 34 1 active sync /dev/sdc2
>
> 2 8 50 - spare /dev/sdd2
>
> # mdadm --grow /dev/md1 --chunk=64K --level=5 --raid-devices=3
> mdadm: New chunk size does not divide component size
>
> -----
> Shouldn't mdadm be able to figure out a way to somehow proceed in this case? :)
> So what if it does not divide, I am increasing the array size by 33%, it
> has plenty of new space, why not leave a bit of it in the end of all devices so
> the chunk size does divide...
> Also I heard of cases (on #linux-raid IRC, I think) when people reshaped like
> this without specifying the chunk size explicitly, and ended up with something
> like a 4K chunk, which is certainly less than optimal.
>
Yes, there is room for improvement here.
The difficulty is that the RAID1 must be converted to a 2-device RAID5 before
devices can be added, and the RAID5 must have a chunk size that is a multiple
of 4K.
Your array cannot even manage 1K.
Newer versions of mdadm will create raid1 arrays to be a multiple of 64K (I
think) so this will be less of a problem.
What you need to do is:
- make sure the filesystem in /dev/md1 doesn't use the last 3k (it probably
uses a 4K block size, so cannot use that last bit
- resize the array down to 488372860K (mdadm -G /dev/md0 --size 488372860)
- convert to a 2-device RAID5 with a 4K chunk size:
mdadm -G /dev/md1 -c 4K -l5 -n2
- convert to a 3-device RAID5 with a 64K chunk size:
mdadm -G /dev/md1 -c 64k -n3
NeilBrown
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