[pve-devel] Snapshot questions

Philipp Marek philipp.marek at linbit.com
Fri Sep 4 08:43:25 CEST 2015


I'm currently implementing the snapshot functions for the DRBD backend; but 
a few questions have popped up, so I'm asking them here.

*) The first question is - how would these get called? "pvesm" shows no 
matching arguments, and the GUI has no "snapshot" buttons either.

Does that hide behind backup functionality or something like that?

*) The second question is - recently the "filesystem_path" function got a new 
line added:

    die "drbd snapshot is not implemented\n" if defined($snapname);

In what circumstances would that function get called? While the Thin LVM 
snapshots that DRBDmanage uses might be addressable locally[1], accessing 
them is not recommended. Is that just for information purposes in the GUI?

*) Thirdly, about restoring snapshots...
There's the volume_snapshot_rollback() function that will destroy the 
volume's data and replace it with the data in the snapshot - but using
a snapshot for a new ("clean") VM isn't being done, right?

During volume_snapshot_rollback() there will no one be accessing the 
original volume, and after rollback it can have a new filesystem_path(),

Thanks for any information!



Ad 1: Or might not, if the given machine doesn't have _that_ snapshot (eg. 
because it was turned off at that time).

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