Growing RAID5 (using RAID0).

[Tony Frank]

Hi there,

On Thu, Feb 26, 2004 at 02:15:14PM +0000, Lewis Thompson wrote:
> I've been thinking about this and I'm wondering if it is possible to do
> something like the following:
> 
>   I have an existing RAID5 volume, comprised of just 3 120GB disks.
> However, I've just bought three more 250GB disks that I also want to
> RAID5.
> 
>   I would still like a single volume, comprising the size of the two
> RAID5 volumes.  Could this be possible through the use of RAID0?

In theory, yes.

> i.e. can I create a RAID0 volume from two RAID5 volumes?

Depends on the raid implementation.

>   I understand this might sound a little odd but if it works it would be
> the ideal solution for me.  I would also be interested in hearing how
> other people might have overcome this problem of growing a large RAID5
> volume.

As you didnt post anything about your implementation I can only guess.
If you are using hardware raid5 for each disk set and it cannot do raid0 
on top you could look at using software raid0 to join the two hardware
sets. Eg vinum can do raid0 in software over raid5 in hardware.
 
If you are doing this purely in software it will depend on what software
you use.  If using vinum I believe you can only mirror across two (or more)
raid5 plexes, so probably not what you want to do.

If you want more specific solutions you will need to advise your hardware
and software details including FreeBSD version.

Regards,

Tony