RE: [Xen-users] Re: DomU on LVM

["Ross S. W. Walker" <rwalker@xxxxxxxxxxxxx>]

Nick Anderson wrote:
> Ross S. W. Walker wrote:
> > Just to poke a little further, why take snapshots in dom0 instead
> > of within domU?
> > 
> > You could provide a second LV to each domU located on different spindles
> > that provide snapshotting within the domUs.
> 
> How will I get a complete point in time snapshot if I am 
> doing LV from inside each domU?

Snapshots of the LVs within a domU will be point in time
in respect of the domU. Basically they work just as if
the domU was a standalone.

> Would it not be introducing unnecessary overhead to do
> LV -> domU(disk) -> 1 partition/disk -> LV
> And do so for each partition you want?

Device mapper, LVM is actually device mapper now, is
an extremely low overhead process that uses the same
techniques as virtual memory mapping to map physical
storage. In fact the page cache integrates tightly
with device mapper to provide robust disk to memory
mapping and access.

There is absolutely no reason these days to not base
all, except removable and backwards compatible,
storage on LVM. Back in the LVMv1 days I would see
your argument, but these days the same device mapper
that handles your software based RAID storage handles
the logical volume management and there is negligiable
performance loss.

-Ross

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