Re: Failed Array Rebuild advice Please

[NeilBrown <neilb@suse.de>]

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On Wed, 11 Apr 2012 19:10:47 -0700 (PDT) jahammonds prost
<gmitch64@yahoo.com> wrote:

> > I think it is best to recover, and then reshape later.
>  
> Which is what I did. The destructive badblocks ran fine overnight, with no errors on the drives that were failed out of the array. Interestingly one of the additional drives that I want to add took an additional 6 hours to run badblocks, so I need to look into that a bit.
>  
> I am having a bit of an issue with the reshape tho... When I try and add one of the 2 additional devices I want to add (I'm going to add them one at a time), I get an error about the bitmap needing to be removed.
>  
>         mdadm --grow /dev/md0 --raid-devices=16
>         mdadm: Need to backup 93184K of critical section..
>         mdadm: Cannot set device shape for /dev/md0: Device or resource busy
>                Bitmap must be removed before shape can be changed
> 
> Now, the docs (and indeed several websites when I googled) suggest that you can have a bitmap present on a grow, and the help suggests that you can even change it during a grow..
> 
> 
>          If the word internal is given, then the bitmap is stored with the metadata on the array, and so is replicated on all devices.  If the word none is given with --grow mode, then any bitmap that is present is removed.
> 
> 
> Is there an issue with the array, or just in my understanding and google foo?

You cannot reshape an array while it has a bitmap attached.
This restriction will probably be removed in Linux 3.5

NeilBrown


> 
> I am running on Centos 6 (2.6.32-220.7.1.el6.x86_64) with madam (mdadm - v3.2.2 - 17th June 2011)
> 
> 
> Thanks again.
> 
> 
> 
>  
> ----- Original Message -----
> From: NeilBrown <neilb@suse.de>
> To: jahammonds prost <gmitch64@yahoo.com>
> Cc: Linux RAID <linux-raid@vger.kernel.org>
> Sent: Wednesday, 11 April 2012, 0:43
> Subject: Re: Failed Array Rebuild advice Please
> 
> On Tue, 10 Apr 2012 21:14:07 -0700 (PDT) jahammonds prost
> <gmitch64@yahoo.com> wrote:
> 
> > One other question as the badblocks progresses.
> >  
> > >  It will then recovery both devices in parallel.
> > 
> > How many additional devices can be done at the same time? I presume that I am going to have to replace the 2 failed devices before I try and grow the array by adding 3 additional drives? I so, how many additional drives can be rebuilt concurrently with a grow? Could I add 5 devices and not see too much of a performance hit? Or would it be more sensible to add them one at a time?
> > 
> 
> I think it is best to recover, and then reshape later.  I cannot promise that
> doing them both at once will work .... it might but I have a feeling that
> there might be problems.
> 
> Adding three additional drives at once should work well enough in terms of
> performance.
> However I would only do it if I were very very confident of the drives.
> If you hit bad blocks you start losing drives, and if you have 3 drives that
> you haven't used before, the chance of losing them all during the reshape -
> while still small - becomes a little too high for comfort.
> 
> But if you have run heavy bad-blocks tests on them all and they appear to
> work, then adding 3 drives at once should be fine.
> 
> NeilBrown


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