Re: add another disk to existing raid 0, ie grow raid 0 possible?

[Nikolay Kichukov <hijacker@oldum.net>]

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Hello Neil,
Here is the result, I think I managed to reproduce it as it has converted the raid0 to raid4.


so commands in sequence:

mdadm --verbose --create /dev/md/mdtest --level=0 --raid-devices=2 --metadata=1.2 /dev/loop0 /dev/loop1
mdadm: chunk size defaults to 512K
mdadm: array /dev/md/mdtest started.

strace -o /tmp/foo -f mdadm --grow /dev/md/mdtest --raid-devices=3 --add /dev/loop2
mdadm: level of /dev/md/mdtest changed to raid4
mdadm: /dev/loop2 not large enough to join array
mdadm: Need to backup 3072K of critical section..
mdadm: /dev/md/mdtest: Cannot grow - need a spare or backup-file to backup critical section
mdadm: aborting level change


The 3 devices are equal sizes, all 200MB in size:

- -rw-r--r--  1 root     root     209715200 Feb 14 11:28 raid_device1.loopback
- -rw-r--r--  1 root     root     209715200 Feb 14 11:28 raid_device2.loopback
- -rw-r--r--  1 root     root     209715200 Feb 14 11:17 raid_device3.loopback


Output of mdadm -E :

http://pastebin.com/WBhgP4L5

Contents of /tmp/foo:

http://pastebin.com/jcietEaa

Let me know if you need any more information to debug this.

Thanks,
- -Nik

On 02/13/2012 12:07 AM, NeilBrown wrote:
> On Fri, 10 Feb 2012 16:10:09 +0200 Nikolay Kichukov <hijacker@oldum.net>
> wrote:
> 
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>> Hi Neil,
>> Do you think it will make sense to try to replicate using loop devices?
> 
> It certainly won't hurt.  It might not achieve anything though.
> Give it a try ... it you manage to reproduce, let me know.
> 
> Thanks,
> NeilBrown
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