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Re: [Xen-users] Stable VBD Types

> I'm currently using snapshotting for backup purposes, snapshotting
> around 20 LVs every 20 minutes and mounting them in dom0.
> I haven't had any problems with this except that with 256M RAM my
> dom0 ran out of kernel memory and an lvcreate operation deadlocked.
> I reported this to the LVM list and was told it was because I had
> too little RAM.  After upgrading dom0 to 512M I have had no such
> problems, although I still am not sure exactly how much RAM each
> snapshot will need.
> Today I saw a question on the linux-lvm list asking if snapshots
> were considered stable in LVM2 now.  Maybe following that thread
> would be more helpful than my anecdotes.

Thanks. Although this is relevent to what I'm wanting to do, what I
meant to say was using lvm snapshots as a way to reduce common files
from repeating on disk. I quote the LVM-HowTo as it explains it a little

"It is also useful for creating volumes for use with Xen. You can create
a disk image, then snapshot it and modify the snapshot for a particular
domU instance. You can then create another snapshot of the original
volume, and modify that one for a different domU instance. Since the
only storage used by a snapshot is blocks that were changed on the
origin or the snapshot, the majority of the volume is shared by the

> How do you mean?  If you start domains that you don't need then the
> RAM is tied up in those domains.  If you wanted some other domain to
> increase its RAM then it may be a laborious process taking a bit of
> RAM from multiple other domains first.  Also the idle processes in
> all those domains would take a small amount of CPU away.  Those are
> about the only problems I can see with running domains you don't
> immediately need.

I mean't as in create them when they are needed, rather than start them




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