Re: re-add POLICY

[NeilBrown <neilb@suse.de>]

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On Sat, 14 Feb 2015 21:59:34 +0000 (UTC) Chris <email.bug@arcor.de> wrote:

> 
> Hi all,
> 
> I'd like mdadm to automatically attempt to re-sync raid members after they
> where temporarily removed from the system. 
> 
> I would have thought "POLICY domain=default action=re-add" should allow this,
> and found a prior post that also seemed to want/test that behaviour.
> But as I understand the answer given there
> http://permalink.gmane.org/gmane.linux.raid/47516
> mdadm is expected to exit with an error (not re-add) upon plugging the
> device back in?
> 
> with:
> mdadm: can only add /dev/loop2 to /dev/md0 as a spare, and force-spare is
> not set.
> mdadm: failed to add /dev/loop2 to existing array /dev/md0: Invalid argument.
> 
> For one, I don't understand what the error messages is trying to tell me, about
> an invalid argument that was never supplied to --incremental?
> 
> But more importantly, how can priorly diconnected devices (marked failed
> with non-future event count) get re-synced automatically when they are 
> plugged in again?
> (avoiding manual mdadm /dev/mdX --add /dev/sdYZ hassle)
> 

Does your array have a write-intent bitmap configured?
If it does, then "POLICY action=re-add" really should work.

If it doesn't, then maybe you need "POLICY action=spare".

This isn't the default, because depending on exactly how/why the device
failed, it may not be safe to treat it as a spare.

If the above does not help, please report:
 - kernel version
 - mdadm version
 - "mdadm --examine" output of at least one good drive and one failed drive.

NeilBrown

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