Kashyap Chamarthy
2012-Sep-13 08:59 UTC
[libvirt-users] After a 'virsh blockpull', 'virsh snapshot-list --tree' o/p does not reflect reality
Hi (Eric?),
A couple of questions while using the 'virsh blockpull'
Summary:
1] Created snapshots this way: base<-snap1<-snap2<-snap3 (online,
external snapshot
--disk-only)
2] I did a 'virsh blockpull' from snap2 into snap3
3] Next, did another 'virsh blockpull' from snap1 into snap3
- Here, 'qemu-img info /path/to/snap3' shows its backing file correctly
as snap1. But not
'virsh snapshot-list $domain --tree' . Any hints?
Detail:
#=========================================#
[root at moon ~]# virsh domblklist daisy --details
Type Device Target Source
------------------------------------------------
file disk vda /export/vmimgs/daisy.qcow2
[root at moon ~]#
#=========================================#
[root at moon ~]# virsh snapshot-create-as daisy snap1-daisy "snap1
description" --diskspec
vda,file=/export/vmimgs/snap1-daisy.qcow2 --disk-only --atomic
Domain snapshot snap1-daisy created
[root at moon ~]#
#=========================================#
[root at moon ~]# virsh snapshot-create-as daisy snap2-daisy "snap2
description" --diskspec
vda,file=/export/vmimgs/snap2-daisy.qcow2 --disk-only --atomic
Domain snapshot snap2-daisy created
[root at moon ~]#
#=========================================#
[root at moon ~]# virsh snapshot-create-as daisy snap3-daisy "snap3
description" --diskspec
vda,file=/export/vmimgs/snap3-daisy.qcow2 --disk-only --atomic
Domain snapshot snap3-daisy created
#=========================================#
[root at moon libvirt-0.10.1-3]# virsh snapshot-list daisy
Name Creation Time State
------------------------------------------------------------
clean-rawhide-f17 2011-12-08 14:34:55 +0530 shutoff
snap1-daisy 2012-09-12 14:58:18 +0530 disk-snapshot
snap2-daisy 2012-09-12 14:59:30 +0530 disk-snapshot
snap3-daisy 2012-09-12 15:00:36 +0530 disk-snapshot
#=========================================#
[root at moon libvirt-0.10.1-3]# virsh snapshot-list daisy --tree
clean-rawhide-f17
snap1-daisy
|
+- snap2-daisy
|
+- snap3-daisy
[root at moon libvirt-0.10.1-3]#
#=========================================#
=> For clarity, listing out the backing files of each image.
#=========================================#
[root at moon libvirt-0.10.1-3]# qemu-img info /export/vmimgs/snap3-daisy.qcow2
image: /export/vmimgs/snap3-daisy.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 129M
cluster_size: 65536
backing file: /export/vmimgs/snap2-daisy.qcow2
#=========================================#
[root at moon libvirt-0.10.1-3]# qemu-img info /export/vmimgs/snap2-daisy.qcow2
image: /export/vmimgs/snap2-daisy.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 3.6M
cluster_size: 65536
backing file: /export/vmimgs/snap1-daisy.qcow2
#=========================================#
[root at moon libvirt-0.10.1-3]# qemu-img info /export/vmimgs/snap1-daisy.qcow2
image: /export/vmimgs/snap1-daisy.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 2.5M
cluster_size: 65536
backing file: /export/vmimgs/daisy.qcow2
[root at moon libvirt-0.10.1-3]#
#=========================================#
=> NOTE: we're pulling snap2 data into snap3, by doing a 'virsh
blockpull' <#=========================================#
[root at moon libvirt-0.10.1-3]# virsh blockpull --domain daisy --path
/export/vmimgs/snap3-daisy.qcow2 --base /export/vmimgs/snap2-daisy.qcow2 --wait
--verbose
Block Pull: [100 %]
Pull complete
[root at moon libvirt-0.10.1-3]#
#=========================================#
[root at moon libvirt-0.10.1-3]# qemu-img info /export/vmimgs/snap3-daisy.qcow2
image: /export/vmimgs/snap3-daisy.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 143M
cluster_size: 65536
backing file: /export/vmimgs/snap2-daisy.qcow2
[root at moon libvirt-0.10.1-3]#
#=========================================#
[root at moon libvirt-0.10.1-3]# virsh snapshot-list daisy --tree
clean-rawhide-f17
snap1-daisy
|
+- snap2-daisy
|
+- snap3-daisy
[root at moon libvirt-0.10.1-3]#
#=========================================#
=> Now, let's pull the data from 'snap1' into 'snap3'
(so that we can make 'snap2'
redundant, and reduce the snapshot chain.
#=========================================#
[root at moon libvirt-0.10.1-3]# virsh blockpull --domain daisy --path
/export/vmimgs/snap3-daisy.qcow2 --base /export/vmimgs/snap1-daisy.qcow2 --wait
--verbose
Block Pull: [100 %]
Pull complete
#=========================================#
NOTE: now the snapshot-tree should flattened (as we pulled the data from snap1
into snap3).
Let's check by running 'qemu-img' . (so the backing-file is now
pointing to snap1, as
expected)
#=========================================#
[root at moon libvirt-0.10.1-3]# qemu-img info /export/vmimgs/snap3-daisy.qcow2
image: /export/vmimgs/snap3-daisy.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 145M
cluster_size: 65536
backing file: /export/vmimgs/snap1-daisy.qcow2
[root at moon libvirt-0.10.1-3]#
#=========================================#
Here, shouldn't 'virsh snapshot-list' --tree be updated as well
?(since 'snap2' is no more
the backing file for 'snap3' ?)
#=========================================#
[root at moon libvirt-0.10.1-3]# virsh snapshot-list daisy --tree
clean-rawhide-f17
snap1-daisy
|
+- snap2-daisy
|
+- snap3-daisy
[root at moon libvirt-0.10.1-3]#
#=========================================#
Version Details:
#=========================================#
[root at moon ~]# rpm -q qemu-kvm libvirt; uname -r
qemu-kvm-1.2-0.2.20120806git3e430569.fc17.x86_64
libvirt-0.10.1-3.fc17.x86_64
3.5.2-3.fc17.x86_64
[root at moon ~]#
#=========================================#
Any ideas why the 'tree' isn't updated yet?
--
/kashyap
Eric Blake
2012-Sep-13 15:26 UTC
[libvirt-users] After a 'virsh blockpull', 'virsh snapshot-list --tree' o/p does not reflect reality
On 09/13/2012 02:59 AM, Kashyap Chamarthy wrote:> Hi (Eric?), > > A couple of questions while using the 'virsh blockpull' > > > > Summary: > > 1] Created snapshots this way: base<-snap1<-snap2<-snap3 (online, external snapshot > --disk-only) > 2] I did a 'virsh blockpull' from snap2 into snap3 > 3] Next, did another 'virsh blockpull' from snap1 into snap3You could have also done a 'virsh blockpull' from snap1 into snap3 without the intermediate pull of snap2, but shouldn't make a difference to your end question.> - Here, 'qemu-img info /path/to/snap3' shows its backing file correctly as snap1. But not > 'virsh snapshot-list $domain --tree' . Any hints?virsh snapshot-list is still accurately listing the state of the tree at the time of the snapshot, not what you have done after the snapshot. If you were to revert to snap1 or snap2 (assuming that I ever get revert-to-disk-snapshots working), you would still be able to do that, provided you haven't deleted snap1 or snap2 from your file system. That is, it is feasible to go from: base<-snap123 (snap1 and snap2 were pulled into snap3) and then revert back to: base<-snap1 (undo the changes that were in snap2 and snap3) Libvirt does not modify any snapshot information when doing a blockpull operation, and I'm not yet convinced that it even needs to. (I'm dreading if it does, because having a blockpull update the snapshot tree seems rather complicated.)> > Here, shouldn't 'virsh snapshot-list' --tree be updated as well ?(since 'snap2' is no more > the backing file for 'snap3' ?)The snapshot chain is independent of each disk's backing chain. The snapshot chain is still correct, because you haven't used 'virsh snapshot-delete' to shorten the snapshot chain (then again, I still haven't implemented that for disk snapshots...) -- Eric Blake eblake at redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 617 bytes Desc: OpenPGP digital signature URL: <http://listman.redhat.com/archives/libvirt-users/attachments/20120913/28c2906e/attachment.sig>