Re: reducing the number of disks a RAID1 expects

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Neil Brown wrote:
2.6.12 does support reducing the number of drives in a raid1, but it
    will only remove drives from the end of the list. e.g. if the
    state was

      58604992 blocks [3/2] [UU_]

then it would work.  But as it is

      58604992 blocks [3/2] [_UU]

it won't.  You could fail the last drive (hdc8) and then add it back
in again.  This would move it to the first slot, but it would cause a
full resync which is a bit of a waste.

Thanks for your help! That's the route I took. It worked ([2/2] [UU]). The only hiccup was that when I rebooted, hdd2 was back in the first slot by itself ([3/1] [U__]). I guess there was some contention in discovery. But all I had to do was physically remove hdd and the remaining two were back to [2/2] [UU].

Since commit 6ea9c07c6c6d1c14d9757dd8470dc4c85bbe9f28 (about
2.6.13-rc4) raid1 will repack the devices to the start of the
list when trying to change the number of devices.

I couldn't find a newer kernel RPM for FC3, and I was nervous about building a new kernel myself and screwing up my system, so I went the slot rotate route instead. It only took about 20 minutes to resync (a lot faster than trying to build a new kernel).

My main concern was that it would discover an unreadable sector while resyncing from the last remaining drive and I would lose the whole array. (That didn't happen, though.) I looked for some mdadm command to check the remaining drive before I failed the last one, to help avoid that worst case scenario, but couldn't find any. Is there some way to do that, for future reference?

Cheers,
11011011
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