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Re: Add a 3rd drive to a existing raid1 (not as spare)

On Tue, Apr 14, 2015 at 11:42:22AM +0200, basti wrote:
> Hello
> I want to add a 3rd drive to a raid 1 array (for disaster backup, the
> drive will be connectet once a week).
> I dry:
> mdadm --add /dev/md1 /dev/sde1
> when I fail the drive there is a message
> FailSpare event detected on md device /dev/md/1, component device /dev/sde1
> How can I add the 3rd drive as "real drive" and not as spare?

Looking at the mdadm manpage (i.e. I've not tried this myself), you
could try being moew explicit about things:

mdadm --add /dev/md1 --raid-devices=3 --spare-devices=0 /dev/sde1

(Note however that the manpage I'm reading - the one in Wheezy - seems a
little unsure whether the option is --raid-devices or --raid-disks).

I think, also, you can convert /dev/sde1 from "spare" to "live" by

mdadm --grow /dev/md1 --raid-devices=3 --spare-devices=0

One last thing to be aware of. If you DO set up your three-disk RAID1
and then take the "backup" drive out of the set, be aware that that will
mark the RAID as "degraded" and expect to get warnings to that effect.

There doesn't appear to be a way to re-mark a device as spare so, to
cleanly remove it, you will need to mark it as faulty (mdadm /dev/md1 -f
/dev/sde1). I don't know, off-hand, if this will affect the backup,

> Best Regards
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