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

[Brian Kroth]

Luis Freitas <lfreitas34 at yahoo.com> 2009-12-11 05:40:
> 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

Just to elaborate on these comments.  Last time I checked CLVM required
the openais/cman cluster stack, which neither heartbeat nor ocfs2 use
(by default).  The userspace stack option for ocfs2 in recent mainline
kernels added support for the openais stack and pacemaker is required to
make heartbeat work with that rather than use it's own cluster stack.

Now, you can do an basic LVM linear span, concatenation, or whatever you
want to call it without any cluster stack, so long as it's not striped
and so long as you heed Sunil's warning about fat fingering changes to
the thing while more than one host is using it.

That means that if you want to add another LUN to the span you can't do
it on the fly.  You have to do something like this:

# On all nodes:
umount /ocfs2

# On all nodes but one:
vgchange -an ocfs2span
# Or, to be extra safe:
halt -p

# On the remaining node:
vgextend ocfs2span /dev/newlun
lvextend -l+100%FREE /dev/mapper/ocfs2span-lv
tunefs.ocfs2 -S /dev/mapper/ocfs2span-lv

# You might actually need the fs mounted for that last bit, I forget.
# Probably a fsck somewhere in there would be wise as well.

# Bring the other nodes back up.

Brian

> --- 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
>   ([1]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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> 
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