[Ocfs2-users] OCFS2 and Snapshots

[Andre Brinkmann]

Michael Wood wrote:
> Andre Brinkmann <brinkman at hni.upb.de> wrote:
>   
>> I am trying to couple OCFS2 with a storage virtualization
>> environment to use features like mirroring and snapshots.
>> Unfortunately it seems to be impossible for ocfs2console (and
>> for mount.ocfs2) to distinguish between the original volume
>> and its snapshot and ocffs2 stops the mount-process with the
>> following messages:
>>     
> [snip]
>   
>> Is it possible too change the uuid and other relevant
>> parameters?
>>     
>
> On Thu, Jul 20, 2006 at 09:29:29AM -0700, Alexei_Roudnev replied:
>   
>> Are you sure, that your snapshort/mirroring software can work
>> on the cluster (shared disks)? I do not know such tools,
>> except parts of Poliserver file system and (possible, with
>> serious limitation) Veritas Volume Manager.
>>     
>
> I am sure he means that he is using something like an HP EVA or
> IBM DS4000 etc. that can do a snapshot of a LUN.  This looks
> like a block for block copy of the original LUN, so if you try
> to mount it, the UUIDs etc. will be identical and OCFS2 will
> complain.
>
> i.e. the snapshot "software" is built into the Storage array and
> does not need to be aware of any clustering.  It just copies (or
> copies on write) the data to another area of disk which can be
> made available to the original machine(s) or to other machines
> entirely.
>
>   
In my case, I am using the built-in disks of my cluster, export them via 
iscsi-target software and
couple them via open-iscsi and our own storage virtualization and 
snapshot software. For OCFS2
(running on the same nodes), there is no distinction between our storage 
implementation and
an HP EVA or IBM DS4000.

Therefore your description hits the critical point. Whatever external 
snapshot solution is used with
OCFS2, you need to be able to change the uuid to use the snapshot and 
the original volume
in the same cluster. Based on the remarks of Joel, I am currently 
looking inside tunefs.ocfs and think
that I will have the feature implemented this evening for evaluation 
purposes.

-- 
-------------------------------------
Dr.-Ing. André Brinkmann

Heinz Nixdorf Institute
University of Paderborn
Fürstenallee 11
33102 Paderborn

Germany
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Email:   brinkman at hni.upb.de
Phone:   +49-5251-60 63 42
Fax:     +49-5251-60 63 51
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