From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sam Bingner <sam@bingner.com>
Subject: Re: Re-shape raid0 acts up
Date: Wed, 10 Jul 2013 12:32:46 +0000
Message-ID: <CE0277FD.1391A%sam@bingner.com>
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To: Ole Tange <tange@binf.ku.dk>, "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>
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On 7/10/13 1:56 AM, "Ole Tange" <tange@binf.ku.dk> wrote:

>I tested reshaping a raid0 on 2 devices to 4 devices.
>
>It seems the reshape first converted to RAID4 and then quickly
>converted to RAID0.
>
>I have now done that on a bigger array. The only change that I am aware
>of is:
>
>* The 2+2 devices are much larger (25 TB each compared to 1 GB each)
>* The system has crashed during the reshape
>
>So right now the system looks like this:
>
>Personalities : [raid6] [raid5] [raid4]
>md3 : active raid4 md1[0] md5[3] md4[4] md2[1]
>      109396484096 blocks super 1.2 level 4, 512k chunk, algorithm 0
>[5/4] [UUUU_]
>
>which looks like the RAID4 just before the final step.
>
>I then tried:
>
># mdadm --grow /dev/md3 -n 4 -l 0 --backup-file reshape.bak
>
>But that seems to cause the reshape to go through the full 100 TB again:
>
>root@lemaitre:/lemaitre-internal# cat /proc/mdstat
>Personalities : [raid6] [raid5] [raid4]
>md3 : active raid4 dm-0[0] dm-3[3] dm-2[4] dm-1[1]
>      109396484096 blocks super 1.2 level 4, 512k chunk, algorithm 0
>[5/4] [UUUU_]
>      [>....................]  reshape =  0.0% (28100/27349121024)
>finish=32428.7min speed=14050K/sec
>
>So I cancelled that and rolled back to the situation before (this was
>possible because I ran this on overlay files):
>
>Personalities : [raid6] [raid5] [raid4]
>md3 : active raid4 md1[0] md5[3] md4[4] md2[1]
>      109396484096 blocks super 1.2 level 4, 512k chunk, algorithm 0
>[5/4] [UUUU_]
>
>Can I convert that to RAID0? Can I do that without having to wait the
>2-3 weeks a full reshape takes?
>

All you need to do to directly convert to RAID0 is:

echo 0 > /sys/block/md3/md/level

Sam