Re: Growing 6 HDD RAID5 to 7 HDD RAID5

["Mathias Burén" <mathias.buren@gmail.com>]

On 12 April 2011 18:14, Roman Mamedov <rm@romanrm.ru> wrote:
> 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
>

Hi,

Yep I mean RAID6, stupid subject line. If I use --layout=preserve ,
what impact will that have? Will the array have redundancy during the
rebuild of the new drive?
If I preserve the layout, what is the final result of the array
compared to not preserving it?

Cheers,
// Mathias
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