[Users] Basic questions about ploop snapshotting

[Simon Barrett]

> I'm not quite following all of your statements. Specifically, I don't
> see why you think you need a base AND a first snapshot. One snapshot is
> sufficient for later restoring. Also, I don't think you need to
> understand the underlying architecture in order to successfully use
> snapshots (it might be helpful or interesting, but not really
> necessary). The command 'snapshot-switch' reliably restores the state of
> the CT it had at the time when you created the snapshot. It's as simple
> as that. Also, when deleting snapshots, vzctl auto-magically does the
> right thing in that it merges or deletes when it is appropriate without
> affecting the other snapshots of the given container.
>

Sorry about kicking this off again, but this hit to me over the weekend and
it cleared things up for me.  Please, someone, correct me if I'm wrong.

As I understand it now, no single file corresponds to a snapshot and to
think of it that way will lead you to do something silly with your data.  A
snapshot is an event.  If you want to think of it in terms of files, it's
the gap between the root.hdd and the delta.  It's a like a HUP in I/O gives
you a spot to go back to.  When you delete a snapshot, you're deleting the
event and this means the files that are either side of that discontinuity
will be merged/healed.

When you mount a snapshot, for example when doing file based backup (
https://openvz.org/Ploop/Backup) you're not actually mounting a snapshot
because there is no snapshot file to mount; you're mounting the
pre-snapshot data.


Simon
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