Ocfs2 users - Dec 2009 - Combining OCFS2 with Linux software RAID-0?

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

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

It should work. All ocfs2 needs is a stable shared storage that
is consistent across all nodes all the time.

Patrick J. LoPresti 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?
>
> Thank you.
>
>  - Pat
>
> _______________________________________________
> Ocfs2-users mailing list
> Ocfs2-users at oss.oracle.com
> http://oss.oracle.com/mailman/listinfo/ocfs2-users
>

Patrick,

?? Depending on what you are using, you could use the volume manager to do the
striping, but you need to use CLVM. So if you can, go for Heartbeat2+CLVM+OCFS2,
all integrated.

?? Not sure but I think Heartbeat2+OCFS2 is only available on the vanilla
kernels, not on the enterprise ones. Maybe Suse has support, I don't know,
you will have to check.

Best Regards,
Luis Freitas

--- On Wed, 12/9/09, Patrick J. LoPresti <lopresti at gmail.com> wrote:

From: Patrick J. LoPresti <lopresti at gmail.com>
Subject: [Ocfs2-users] Combining OCFS2 with Linux software RAID-0?
To: ocfs2-users at oss.oracle.com, linux-raid at vger.kernel.org
Date: Wednesday, December 9, 2009, 9:03 PM

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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