Date: Thu, 23 Mar 2017 17:09:08 -0400
To: Stephen Mueller <stephen@mueller.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: RAID array is gone, please help
Message-ID: <20170323210908.GQ14186@csclub.uwaterloo.ca>
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From: lsorense@csclub.uwaterloo.ca (Lennart Sorensen)
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On Thu, Mar 23, 2017 at 10:02:23PM +0100, Stephen Mueller wrote:
> Looks like it worked! Thanks!

Well at least you could backup the data, just in case.

> I used:
> 
> sudo mdadm --create /dev/md0 --assume-clean --verbose --level-10
> --raid-devices=4 /dev/sdc /dev/sdd /dev/sde /dev/sdf

I wonder about the assume-clean, but I would think any data you wrote
will have been duplicated at the time you wrote it, and only unused
space might not have been synced yet.

Maybe running a forced resync would be worthwhile.

> And I got my instructions for creating the array here, and they
> also don't use partitions...
> 
> https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-16-04

Well it works, as long as you don't leave anything around to confuse it,
in this case a GPT partition table that somehow came back to bite you.

I wonder if mdadm could perhaps warn about the existing partition table
when being asked to create a new device.

Does it survive reboots now?

-- 
Len Sorensen