Re: [ovirt-users] How long can a disk snapshot exist for?
- Original Message - From: Ryan Groten ryan.gro...@stantec.com To: Vered Volansky ve...@redhat.com, users users@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:ve...@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.gro...@stantec.com To: Vered Volansky ve...@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:ve...@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.gro...@stantec.com To: users@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@ovirt.org http://lists.ovirt.org/mailman/listinfo/users ___ Users mailing list Users@ovirt.org http://lists.ovirt.org/mailman/listinfo/users ___ Users mailing list Users@ovirt.org http://lists.ovirt.org/mailman/listinfo/users
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.gro...@stantec.com To: Vered Volansky ve...@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:ve...@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.gro...@stantec.com To: users@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@ovirt.org http://lists.ovirt.org/mailman/listinfo/users ___ Users mailing list Users@ovirt.org http://lists.ovirt.org/mailman/listinfo/users
Re: [ovirt-users] How long can a disk snapshot exist for?
Thanks that's exactly the explanation I was looking for. -Original Message- From: Vered Volansky [mailto:ve...@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.gro...@stantec.com To: Vered Volansky ve...@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:ve...@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.gro...@stantec.com To: users@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@ovirt.org http://lists.ovirt.org/mailman/listinfo/users ___ Users mailing list Users@ovirt.org http://lists.ovirt.org/mailman/listinfo/users
[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@ovirt.org http://lists.ovirt.org/mailman/listinfo/users
