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?

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 <redacted>
To: jahammonds prost <redacted>
Cc: Linux RAID <redacted>
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
[off-list ref] wrote:

One other question as the badblocks progresses.
 

quoted

 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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