9:05 p.m.
Thanks a lot for the details.
From http://wiki.libvirt.org/page/Snapshots, we have to pause the domain before taking
snapshot and resume after. Is there any way to do "live" snapshotting for
running domain or reduce pause time?
Thanks,
Lei
------------------ Original ------------------
From: "Eric Blake"<eblake(a)redhat.com>;
Date: Wed, Jun 6, 2012 08:24 PM
To: "SimpleCloud"<simplecloud(a)qq.com>;
Cc: "libvirt-users"<libvirt-users(a)redhat.com>;
Subject: Re: [libvirt-users] The default location of vm snapshots
On 06/06/2012 03:20 AM, SimpleCloud wrote:
Hi all,
Where could I find the memory dump and disk snapshots for vm after command "virsh
snapshot-create <some_running_vm>"? Thanks in advance.
This particular form of snapshot is called the 'system checkpoint'
snapshot, and the current qemu implementation is that the snapshot
creates internal snapshots in your qcow2 files. If you do 'qemu-img
info $path_to_img', you will see the disk snapshots listed as internal
snapshots for each image associated with the domain, as well as the
first qcow2 file also having memory associated with the internal snapshot.
I found the xml files in /var/lib/libvirt/qemu/snapshot/, but hava no idea about the raw
snapshot file.
Looking in /var/lib/libvirt is generally unsupported (that is an
internal libvirt detail, and subject to change in future releases). The
only way to safely look at the snapshot XML is via the API
(virDomainSnapshotGetXMLDesc, which is wrapped by 'virsh snapshot-dumpxml').
I am also hoping to submit a patch that will allow you the option to
create an external snapshot rather than using qcow2 internal snapshots,
but that's not in the code base yet.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
9:57 p.m.
New subject: [libvirt-users] The default location of vm snapshots
On 06/06/2012 07:05 AM, SimpleCloud wrote:
Thanks a lot for the details.
From http://wiki.libvirt.org/page/Snapshots, we have to pause the domain before taking
snapshot and resume after.
Actually, you don't have to do it yourself; libvirt takes care of doing
it for you if that's what qemu requires, as part of the libvirt snapshot
comand.
Is there any way to do "live" snapshotting for running
domain or reduce pause time?
You can do 'disk-only' snapshots instead of system checkpoints, which
are much faster (less than 1 second, while system checkpoints can be
seconds or even minutes long). And I'm also hoping to add code that
will support external system checkpoints by doing a live migration to
file coupled with a disk snapshot, which will hopefully reduce guest
downtime compared to the current mandatory guest downtime of the qemu
'savevm' monitor command, but it may require qemu to implement more
features first.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
8:22 a.m.
New subject: [libvirt-users] The default location of vm snapshots
you could try: snapshot-create-as guest guestsnap --disk-only
Thanks.
--Xingxing Gao
2012/6/6 Eric Blake <eblake(a)redhat.com>:
On 06/06/2012 07:05 AM, SimpleCloud wrote:
> Thanks a lot for the details.
>
>
> From http://wiki.libvirt.org/page/Snapshots, we have to pause the domain before
taking snapshot and resume after.
Actually, you don't have to do it yourself; libvirt takes care of doing
it for you if that's what qemu requires, as part of the libvirt snapshot
comand.
> Is there any way to do "live" snapshotting for running domain or reduce
pause time?
You can do 'disk-only' snapshots instead of system checkpoints, which
are much faster (less than 1 second, while system checkpoints can be
seconds or even minutes long). And I'm also hoping to add code that
will support external system checkpoints by doing a live migration to
file coupled with a disk snapshot, which will hopefully reduce guest
downtime compared to the current mandatory guest downtime of the qemu
'savevm' monitor command, but it may require qemu to implement more
features first.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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11:05 a.m.
New subject: [libvirt-users] The default location of vm snapshots
[please don't top-post on technical lists]
On 06/06/2012 06:22 PM, Xing.x.Gao wrote:
you could try: snapshot-create-as guest guestsnap --disk-only
Yes, this is...
>
>> Is there any way to do "live" snapshotting for running domain or reduce
pause time?
>
> You can do 'disk-only' snapshots instead of system checkpoints, which
> are much faster
...precisely what I meant by 'disk-only' snapshots. As long as you
don't need the associated VM state (that is, if you are okay that
reverting to the snapshot implies that any in-flight memory that has not
been flushed to disk will be lost, and that the disks will probably need
fsck), then this is indeed the way to go.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
4475
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3 comments
3 participants
participants (3)
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Eric Blake -
SimpleCloud -
Xing.x.Gao