Re: Growing 6 HDD RAID5 to 7 HDD RAID5

[Roman Mamedov <rm@romanrm.ru>]

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On Tue, 12 Apr 2011 17:56:05 +0100
Mathias Burén <mathias.buren@gmail.com> wrote:

> I'm approaching over 6.5TB of data, and with an array this large I'd
> like to migrate to RAID6 for a bit more safety.

That's a great decision (and I suppose you made a typo in the subject).
RAID5 is downright dangerous at that disk count, and with disks of that size.

> I'm just checking if I
> understand this correctly, this is how to do it:
> 
> * Add a HDD to the array as a hot spare:
> mdadm --manage /dev/md0 --add /dev/sdh1
> 
> * Migrate the array to RAID6:
> mdadm --grow /dev/md0 --raid-devices 7 --level 6

Looks correct to me...

The first command can be just "mdadm --add /dev/md0 /dev/sdh1".

If you'd rather avoid a reshape at this point, you can add
"--layout=preserve" to the second line. That way you will have just a rebuild
of the new drive, instead of a full reshape.

You will also need to "--grow --bitmap=none" first (you can re-add the bitmap
later).

-- 
With respect,
Roman

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