Re: [Xen-users] Hot Copy file based VMs

[Javier Guerra <javier@xxxxxxxxxxx>]

On Wed, Mar 18, 2009 at 10:46 AM, Jan Kalcic <jandot@xxxxxxxxxxxxxx> wrote:
>
> What do you mean with "atomic" copy?
>

when talking about storage (or data access in general), an operation
is 'atomic' from some point of view if it's 'indivisible'. that is,
there wasn't any point in time when it was 'halfway done'.

LVM snapshots manage this, because it's not a real copy (it's more
like a fork, but it works like a copy in most cases), and because it
taps the main stream of storage operations.

most other kinds of copy can't be really atomic, that's why Fajar
tells you to suspend the guest while you do the copy.  that way, even
if there was a time when the copy was half-done, the guest wasn't
really there, so from it's point of view, the copy was atomic.

-- 
Javier

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