Re: Growing a raid 6 array

[Louis-David Mitterrand <vindex+lists-linux-raid@apartia.org>]

On Fri, Apr 13, 2007 at 10:15:05AM +0200, Laurent CARON wrote:
> Neil Brown a écrit :
> > On Thursday March 1, jpiszcz@lucidpixels.com wrote:
> >> You can only grow a RAID5 array in Linux as of 2.6.20 AFAIK.
> > 
> > There are two dimensions for growth.
> > You can increase the amount of each device that is used, or you can
> > increase the number of devices.
> > 
> > You are correct that increasing the number of devices only works for
> > RAID5 (and RAID1, but you don't get extra space) in 2.6.20 (RAID6
> > coming in 2.6.21).
> > 
> > However this question is about growing an array the first way:
> > increasing the amount of space used on each devices, and that is
> > supported for RAID1/4/5/6.
> > 
> > And Laurent:
> >   1/ Yes, it is that easy
> >   2/ I doubt a nearly-full ext3 array increases the risk
> >   3/ The effect of adding a bitmap is that if you suffer a crash while
> >      the array is degraded, it will resync faster so you have less
> >      exposure to multiple failure.
> 
> I just finished changing disks, growing the array, and then the filesystem.
> 
> It worked flawlessy.
> 
> Just a little notice: I had to unmount my ext3 filesystem to be able to
> resize it. (Took ~8 hours to fsck + resize the 15 disks array from 6 to
> 9TB on a dual Xeon with 4GB RAM).

FWIW:

I changed a 6 x 400G system to 500G disks and grew the raid5 array. It 
worked fine save for these warnings:

	Apr  8 16:54:33 sylla mdadm: RebuildStarted event detected on md device /dev/md1
	Apr  8 16:54:33 sylla mdadm: Rebuild20 event detected on md device /dev/md1
	Apr  8 16:54:33 sylla mdadm: Rebuild40 event detected on md device /dev/md1
	Apr  8 16:54:33 sylla mdadm: Rebuild60 event detected on md device /dev/md1
	Apr  8 16:54:33 sylla mdadm: Rebuild80 event detected on md device /dev/md1
	Apr  8 16:54:33 sylla kernel: md1: invalid bitmap page request: 187 (> 186)
	Apr  8 16:54:33 sylla kernel: md1: invalid bitmap page request: 187 (> 186)

	etc...

So after rebooting I removed the bitmap and recreated it.

Online resizing of the 2.0T xfs to 2.4T only took a few _seconds_.

A similar operation on a 4 x 250G raid5 system upgraded to 400G disks 
with reiser3 also took a few seconds of _online_ time.

Kernel 2.6.20.6
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