[ClusterLabs] Antw: VirtualDomain as resources and OCFS2

[Ulrich Windl]

>>> "Lentes, Bernd" <bernd.lentes at helmholtz-muenchen.de> schrieb am 10.09.2018
um
18:20 in Nachricht
<719144896.5605540.1536596432401.JavaMail.zimbra at helmholtz-muenchen.de>:
> Hi,
> 
> i'm establishing a cluster with virtual guests as resources which should 
> reside in a raw files on OCFS2 formatted logical volumes.
> My first idea was to create for each VirtualDomain its own logical volume, i

> thought that would be well-structured. 
> But now i realize that my cluster configuration gets confusing. E.g. i need

> for each OCFS2 Volume a resource, which must be cloned and which has an
order 
> with its respective guest. I'm having about 10 Virtual Domains. 10 
> VirtualDomain resources, 10 clones, 10 orders. Confusing.
> Now i'm thinking of one Logical Volume for all VirtualDomains. Then the 
> cluster configuration would be more overseeable. Just one OCFS2 resource, 
> just one clone, just one order. 
> Is there any reason which contradicts to the use of only one LV and one 
> OCFS2 resource for several VirtualDomains ?

Hi Bernd,

the disappointing answer ist this: With cLVM you cannot make snapshots of the
LVs (easily), and in SLES11 SP4 at least the tool to make snapshots of OCFS2
also isn't provided. So the major advantage of having separate LVs for each VM
is actually gone, making a desaster recovery strategy somewhat difficult. We do
backups of the files "inside" the VM (just like a physical machine), but once
your VM images are gone, desaster recovery is a bit tricky, however.

Maybe it is most efficient to have a SAN-provided "physical" disk for each VM.
The if the SAN can make snapshots of those disks, you have an elegant backup
and recovery solution. We had "kind of that" (using iSCSI-provided disks) about
15 years ago in SLES10, but the solution was unable to allow loive migration (a
different and longer story)...

Regards,
Ulrich


> 
> Thanks.
> 
> 
> Bernd
> 
> -- 
> 
> Bernd Lentes 
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