[Ocfs2-users] Combining OCFS2 with Linux software RAID-0?

[Neil Brown]

On Wed, 9 Dec 2009 15:03:11 -0800
"Patrick J. LoPresti" <lopresti at gmail.com> wrote:

> Is it possible to run an OCFS2 file system on top of Linux software RAID?
> 
> Here is my situation.  I have four identical disk chassis that perform
> hardware RAID internally.  Each chassis has a pair of fiber channel
> ports, and I can assign the same LUN to both ports.  I want to connect
> all of these chassis to two Linux systems.  I want the two Linux
> systems to share a file system that is striped across all four chassis
> for performance.
> 
> I know I can use software RAID (mdadm) to do RAID-0 striping across
> the four chassis on a single machine; I have tried this, it works
> fine, and the performance is tremendous.  I also know I can use OCFS2
> to create a single filesystem on a single chassis that is shared
> between my two Linux systems.  What I want is to combine these two
> things.
> 
> Suse's documentation
> (http://www.novell.com/documentation/sles11/stor_admin/?page=/documentation/sles11/stor_admin/data/raidyast.html)
> says:
> 
> "IMPORTANT:Software RAID is not supported underneath clustered file
> systems such as OCFS2, because RAID does not support concurrent
> activation. If you want RAID for OCFS2, you need the RAID to be
> handled by the storage subsystem."
> 
> Because my disk chassis already perform hardware RAID-5, I only need
> Linux to do the striping (RAID-0) in software.  So for me, there is no
> issue about "which node should rebuild the RAID" etc.  I understand
> that Linux md stores meta-data on the partitions and is not cluster
> aware, but will this create problems for OCFS2 even if it is just RAID
> 0?
> 
> Has anybody tried something like this?  Are there alternative RAID-0
> solutions for Linux that would be expected to work?


For RAID0 or LINEAR, this should work - give it a try.

If it doesn't work in some way, let me know and I'll see about fixing it.

It might work for RAID1 one day to, but is unlikely to ever work for 
RAID5.

NeilBrown