[ovirt-users] How long can a disk snapshot exist for?

[Vered Volansky]

Hi Ryan,

Should have replied to all, my bad.
See my answer embedded below:

----- Original Message -----
> From: "Ryan Groten" <Ryan.Groten at stantec.com>
> To: "Vered Volansky" <vered at redhat.com>
> Sent: Thursday, August 28, 2014 5:50:12 PM
> Subject: RE: [ovirt-users]  How long can a disk snapshot exist for?
> 
> Thanks for the reply!  So when keeping a snapshot for a long time I have to
> keep an eye on how large it will get over time.
The snapshot's size itself is determined when it's taken according to the disks size at the time.
It then stays the same.
When taking a snapshot, the active image of the disk is "frozen" at this point in time, and a new, empty active image is created to hold the new data on the disk.
The new data is saved in the form of diffs, so if there are mainly additions to the snapshot time, the space difference of the snapshot is negligible.
But if the diffs include many reductions from the snapshot's state - this might consume a lot of space, again, depending on your usage.
Note that you're also limited by the disk's size.

  But there's no (or very
> little) performance impact or potential issues from keeping snapshots (other
> than the storage pool filling up maybe)?
All the vm operations take into consideration snapshots. Storage is an issue, but so is every operation you'll make on the vm.
When you have one image, the vm is handled only through this image. But when you have several, for each operation the right layer will search for the existence/ability to do the operation in all the snapshots (worst case).
So there is in fact an impact, but it's due to the mere existence of the snapshots and their number, not their age.
We support 26 snapshots per VM, but you should only use it if you actually need the backup.
If you need RT performance, try to avoid it as possible.

> 
> Thanks,
> Ryan
> 
> -----Original Message-----
> From: Vered Volansky [mailto:vered at redhat.com]
> Sent: August-27-14 11:19 PM
> To: Groten, Ryan
> Subject: Re: [ovirt-users] How long can a disk snapshot exist for?
> 
> Ryan,
> 
> Disk snapshots consume fixed storage space (fixed since time of creation).
> The more differences there are from on your disk since the snapshot was
> taken, the more space is consumed, but that happens with no relation to the
> snapshot.
> If your frequent changes are in the form of adding data to you disks (on top
> of data snapshot time), then the space consumption of the snapshot is
> negligible.
> If you are undoing stuff from the snapshot time, there is actually more space
> consumed (to save the differences), otherwise the space would have just been
> released.
> 
> Vered
> 
> 
> ----- Original Message -----
> > From: "Ryan Groten" <Ryan.Groten at stantec.com>
> > To: users at ovirt.org
> > Sent: Thursday, August 28, 2014 12:49:02 AM
> > Subject: [ovirt-users]  How long can a disk snapshot exist for?
> > 
> > 
> > 
> > Is there any limit/performance considerations to keeping a disk
> > snapshot for extended periods of time? What if the disk is changing
> > frequently vs mostly static?
> > 
> > 
> > 
> > Thanks,
> > 
> > Ryan
> > 
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>