Re: RAID6 chunk size change?

Mark Knecht <markknecht@xxxxxxxxx> · Sun, 23 Jan 2011 11:10:40 -0800

On Sun, Jan 23, 2011 at 10:53 AM, Mark Knecht <markknecht@xxxxxxxxx> wrote:
> Hi,
> Â I've got an existing (and well backed up as of a couple of minutes
> ago) 5-drive RAID6 shown here:
>
> c2stable ~ # mdadm --detail /dev/md7
> /dev/md7:
> Â Â Â ÂVersion : 1.2
> ÂCreation Time : Sun Jan 16 17:02:24 2011
> Â Â Raid Level : raid6
> Â Â Array Size : 395387904 (377.07 GiB 404.88 GB)
> ÂUsed Dev Size : 131795968 (125.69 GiB 134.96 GB)
> Â Raid Devices : 5
> ÂTotal Devices : 5
> Â ÂPersistence : Superblock is persistent
>
> Â ÂUpdate Time : Sun Jan 23 10:25:41 2011
> Â Â Â Â ÂState : clean
> ÂActive Devices : 5
> Working Devices : 5
> ÂFailed Devices : 0
> ÂSpare Devices : 0
>
> Â Â Â Â Layout : left-symmetric
> Â Â Chunk Size : 512K
>
> Â Â Â Â Â Name : c2stable:7 Â(local to host c2stable)
> Â Â Â Â Â UUID : ded5e0c6:1a5a73ad:01949557:bb4e015a
> Â Â Â Â Events : 17
>
> Â ÂNumber Â Major Â Minor Â RaidDevice State
> Â Â Â 0 Â Â Â 8 Â Â Â Â7 Â Â Â Â0 Â Â Âactive sync Â /dev/sda7
> Â Â Â 1 Â Â Â 8 Â Â Â 23 Â Â Â Â1 Â Â Âactive sync Â /dev/sdb7
> Â Â Â 2 Â Â Â 8 Â Â Â 39 Â Â Â Â2 Â Â Âactive sync Â /dev/sdc7
> Â Â Â 3 Â Â Â 8 Â Â Â 50 Â Â Â Â3 Â Â Âactive sync Â /dev/sdd2
> Â Â Â 4 Â Â Â 8 Â Â Â 66 Â Â Â Â4 Â Â Âactive sync Â /dev/sde2
> c2stable ~ #
>
> Â I would like to change this RAID to a smaller chunk size. (16K for
> now) What is the right command to use?
>
> Â From Google and the mdadm man pages I'm coming up with something like:
>
> mdadm --grow /dev/md7 --level=6 --chunk=16 --backup-file=/root/backup-md7
>
> Maybe I don't need --level because the level isn't changing? Neither
> is the number of drives.
>
> Thanks in advance,
> Mark
>

OK, I found a blog of Neil's in which I had read the top but hadn't
gone through the comments:

http://neil.brown.name/blog/20090817000931
It seems he answers my question further down in the comments.

Looks like

mdadm --grow /dev/md7 --chunk=16

would be enough.

Cheers,
Mark
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html