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

Patrick J. LoPresti lopresti at gmail.com
Wed Dec 9 15:03:11 PST 2009


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?

Thank you.

 - Pat



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