Re: permanently removing a spare

[NeilBrown <neilb@suse.de>]

On Tue, 17 May 2011 15:09:18 -0400 Tobias McNulty <tobias@caktusgroup.com>
wrote:

> On Wed, May 11, 2011 at 9:49 PM, Tobias McNulty <tobias@caktusgroup.com> wrote:
> >
> > Hi all,
> >
> > After successfully converting my raid6 array to raid5, I of course
> > neglected to update mdadm.conf, so the array was absent on reboot.  A
> > quick mdadm --assemble brought the array back online.
> >
> > However, now I am trying to update mdadm.conf, and I hit what I think
> > is this bug:
> >
> > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=610184
> >
> > So I thought I'd try to remove the spare from my raid5 array.  I
> > marked it as failed and then removed it, and the spare no longer shows
> > in /proc/mdstat:
> >
> > md0 : active raid5 sda[0] sdd[3] sdc[2] sdb[1]
> >      5860543488 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
> >
> > However, when I do mdadm -Es, I still see it:
> >
> > ARRAY /dev/md0 UUID=25a818ff:68f07e28:0d7656f3:2f233380
> >   spares=1
> >
> > And I still see the "error: superfluous RAID member (4 found)." error
> > when running update-grub (even if I leave out the spares=1 part).
> >
> > Is there a way to "permanently" remove the spare "slot" from the
> > array?  I tried mdadm --grow --spare-devices=0, since the man page
> > arguably suggests that --spare-devices should work in grow mode, but
> > running the command reports that it's not actually supported.  To the
> > credit of the man page, the description of --spare-devices *does* say
> > it is used in the *initial* array creation.
> >
> > Does what I'm trying to do make sense?  Is there a way to make the
> > array forget that it ever had a spare in the first place?
> >
> > I'm a little afraid to reboot until I get this figured out.
> 
> Hey all - I think I am missing something obvious but I am not sure
> what it is, and I still haven't turned up anything in my own
> searching.
> 
> Do you have any advice for what I need to do so that the array is
> mounted automatically on boot again?
>

If you want to stop a spare from looking like part of the array, simply

   mdadm --zero-superblock /dev/DEVICENAME

But you really want it to assemble automatically at boot and I cannot see how
a spare would interfere with that, bugs.debian.org isn't responding just now.

NeilBrown
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