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"Benoit St-Pierre" 08-27-2008 07:00 PM

RAID with mixed drive sizes
 
I'm in the planning stages of setting up a file server and am considering using RAID.

My concern is that my drive sizes are mixed. I have two 500GB SATA drives, a 320GB IDE and a 250GB IDE.


I would like to set these up so that the maximum amount of disk space is usable, but still be able to recover from any one drive failing. I would also like to be able to add drives of any size as easily as possible.


Is it possible to split each disk into a bunch of 10GB partitions, giving me 157 partitions in total, and specifying that I want to have 50 partitions worth of parity info so that if any 50 partitions go bad (ie: one of the 500GB disks) the RAID can recover? Adding/replacing would be simple if I can change the amount of parity info to keep, but I don't know if this is actually possible. It looks as though spares need to be explicitly given so, if a disk with lots of spares goes down, it's not going to work.


Another option I see is if I create 4x 250GB partitions (one on each drive) in one RAID5 array, 3x 70GB partitions (on the 3 larger drives) in another RAID5 array, and two 120GB in a RAID1 array. The RAID1 array reduces my total available disk space a bit, which is less than ideal and adding/replacing disks would be more of a headache.


I remember reading something about using LVM and RAID to achieve this, but everything I've found has been for identical drives.

Any suggestions?

Xav' 08-27-2008 07:20 PM

RAID with mixed drive sizes
 
On Wednesday 27 August 2008 21:00:11 Benoit St-Pierre, you wrote*:

> I'm in the planning stages of setting up a file server and am considering
> using RAID.
>
> My concern is that my drive sizes are mixed. I have two 500GB SATA drives,
> a 320GB IDE and a 250GB IDE.
>
> I would like to set these up so that the maximum amount of disk space is
> usable, but still be able to recover from any one drive failing. I would
> also like to be able to add drives of any size as easily as possible.
>
> Is it possible to split each disk into a bunch of 10GB partitions, giving
> me 157 partitions in total, and specifying that I want to have 50
> partitions worth of parity info so that if any 50 partitions go bad (ie:
> one of the 500GB disks) the RAID can recover? Adding/replacing would be
> simple if I can change the amount of parity info to keep, but I don't know
> if this is actually possible. It looks as though spares need to be
> explicitly given so, if a disk with lots of spares goes down, it's not
> going to work.

AFAIK, it's not possible to have so much partitions under linux, but i can't
remember the maximum of supported partitions... but good luck to manage a so
wide number of partitions !

> Another option I see is if I create 4x 250GB partitions (one on each drive)
> in one RAID5 array, 3x 70GB partitions (on the 3 larger drives) in another
> RAID5 array, and two 120GB in a RAID1 array. The RAID1 array reduces my
> total available disk space a bit, which is less than ideal and
> adding/replacing disks would be more of a headache.

IMHO, i think this could be a solution. This is possible using software RAID as
it's in the kernel, and then reassemble created raid partitions in one LVM
volume group, so you can use partitions of any space !

> I remember reading something about using LVM and RAID to achieve this, but
> everything I've found has been for identical drives.
>
> Any suggestions?

HTH.

Xavier Parizet


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