[Users] Basic questions about ploop snapshotting

Scott Dowdle dowdle at montanalinux.org
Thu Oct 16 15:38:44 PDT 2014


Greetings,

----- Original Message -----
> I think I'm having some brainfart moment on how snapshots really
> function.

Ok, I played with it... and I *THINK* I understand it now.

Your first snapshot is like a base... and you have to have additional snapshots above your base... or you can't rollbackup.

So, if the correct way to do what I wanted to do is:

vzctl snapshot {ctid} --skip-suspend --skip-config --name base
 (a snapshot named base gets created)

Now I can make second snapshot to work on:
vzctl snapshot {ctid} --skip-suspend --skip-config --name zimbra806
 (a second snapshot named zimbra806 is created)

Now I can do my upgrade attempt...
If it doesn't go well, I would want to:
  vzctl snapshot-switch {ctid} --id {id-for-base}
That would switch it to the base and zimbra 806 would be inactive and I could then:
  vzctl snapshot-delete {ctid} --id {id-for-zimbra806}
  That deletes the snapshot named zimbra806 *WITHOUT* merging down.

If the upgrade *DOES* go well... and I want to make the active snapshot my new base I can:
(assuming the active snapshot is zimbra806 and I didn't switch back to base)
  vzctl snapshot-delete {ctid} --id {id-for-zimbra806}
That would merge down the data from zimbra806 to base before deleting zimbra806.

One thing to note about deleting snapshots... if you want to delete a snapshot *WITHOUT* merging data down... it has to be inactive without any other snapshot depending on it.  If you try to delete a snapshot that is active or has other snapshots depending in it... it will merge down before deleting.

Is that correct?  That's how it appears to work to me.  You *REALLY* have to know what you are doing to get the desired results.

- - - - - -

I do have a separate question... and that is... when working with OpenVZ and snapshots I've been using the vzctl command's snapshot features and have *NOT* tried using the ploop command directly.  The ploop command does have a snapshot-merge parameter whereas vzctl doesn't.  I'm not sure if it is recommended to use the ploop command directly.  I think I'll stick with using vzctl as the interface to ploop snapshots.  Oh, I forgot to put a question in there.  Hmmm, I guess my question is:

When dealing with ploop-based OpenVZ containers... is it recommended to use vzctl as the ploop interface and avoid the ploop command... or is it ok to ploop directly?  The idea of using the ploop command directly is scary to me for some reason.

TYL,
-- 
Scott Dowdle
704 Church Street
Belgrade, MT 59714
(406)388-0827 [home]
(406)994-3931 [work]


More information about the Users mailing list