Re: Can't reshape RAID1 to RAID5 due to chunk size

[Roman Mamedov <rm@romanrm.ru>]

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On Wed, 19 Sep 2012 16:20:58 +1000
NeilBrown <neilb@suse.de> wrote:

> What you need to do is:
>   - make sure the filesystem in /dev/md1 doesn't use the last 3k (it probably 
>     uses a 4K block size, so cannot use that last bit
>   - resize the array down to 488372860K  (mdadm -G /dev/md0 --size 488372860)
>   - convert to a 2-device RAID5 with a 4K chunk size:
>       mdadm -G /dev/md1 -c 4K -l5 -n2
>   - convert to a 3-device RAID5 with a 64K chunk size:
>       mdadm -G /dev/md1 -c 64k -n3
> 
> NeilBrown

Thanks, Neil.

I have since finished this migration in another way, luckily I had some spare
drives lying around, so had an option to create a separate RAID5 from scratch
and move over & replace the drives one by one.

By the way the "want_replacement" feature is totally awesome, thanks to it at
no point in my operations I was left without redundancy (after all a N-disk
degraded RAID5 reliability-wise is like a RAID0 of N disks, and that's
something I wanted to avoid having even for a short period).

-- 
With respect,
Roman

~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Stallman had a printer,
with code he could not see.
So he began to tinker,
and set the software free."

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