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

[Vered Volansky]

----- Original Message -----
> From: "Ryan Groten" <Ryan.Groten at stantec.com>
> To: "Vered Volansky" <vered at redhat.com>, "users" <users at ovirt.org>
> Sent: Thursday, August 28, 2014 7:53:17 PM
> Subject: Re: [ovirt-users] How long can a disk snapshot exist for?
> 
> Thanks that's exactly the explanation I was looking for.
Sure, happy to help :)
> 
> -----Original Message-----
> From: Vered Volansky [mailto:vered at redhat.com]
> Sent: August-28-14 9:29 AM
> To: Groten, Ryan; users
> Subject: Re: [ovirt-users] How long can a disk snapshot exist for?
> 
> 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
> > > 
> > > _______________________________________________
> > > Users mailing list
> > > Users at ovirt.org
> > > http://lists.ovirt.org/mailman/listinfo/users
> > > 
> > 
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