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Re: [Xen-users] xen storage options - plase advise

> James,
> I had similar questions a while ago and back then the consensus was that
> snapshotting a running domU does *not* provide a consistent backup.  This
> is especially the case with databases and applications which do not
> immediately flush writes to disk.  I believe XenServer may do a better
> job, but I am unsure on this.
> Basically, the only way to do a proper backup is to properly shutdown the
> domU before taking the snapshot, thus ensuring there is no chance of
> losing data.  For some people not doing this is an acceptable risk and
> certainly better than no backup at all.
> With regard to storage, the industry buzzword for what you describe is
> 'thin provisioning'.  This, together with the de-duplication features
> offered by some SANs makes for very efficient use of storage space.  If I
> do this with Solaris for example, it shouldn't really matter if I use a
> file system or LVM on the exported volume, because all I am doing is
> telling ZFS to export a zvol and the dom0 sees this as block-level
> storage.  I might set the maximum size of the volume to much more than the
> space currently available and as it fills up I just need to ensure I keep
> pace and add more physical storage as needed.  Your SAN product may well
> allow you to do the same thing.  The advantage of LVM is that you can
> later add further space with minimal hassle.
> If you need to use CLVM and lose LVM snapshots, could you take snapshots
> directly from your SAN instead?
> Hope this helps,
> Matt.

I've read that snapshotting is not a reliable way of doing backups on
this list before. I believe the term was you would end up with a dirty
file system. Most of the systems I run, I think snapshotting would
probably be ok in a recovery situation, as long as they boot. 

Up to this point I treat my domUs as standalone machines running backup
software. Recovery is not as easy. We do mirror our SAN in case of
catastrophic failure, but obviously this is not snapshotting.

I'm still left with the same questions about usage of space. Can I use
LVM or CLVM as one large storage repository that is mounted on each
dom0? Then use this space to store file based domUs? 


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