9:28 p.m.
I would like to make a snapshot of a running VM, let it continue to run after the
shapshot, and then at some later time roll back the VM to that previous running state. Can
I do that with libvirt? If so, how? I understand that this will cause all kinds of havoc
with things like ongoing TCP connections, and I accept that risk.
--
Gary Jackson
9:56 p.m.
On Tue, Sep 19, 2017 at 01:28:45PM +0000, Jackson, Gary L. wrote:
I would like to make a snapshot of a running VM, let it continue to run
after the shapshot, and then at some later time roll back the VM to
that previous running state. Can I do that with libvirt? If so, how? I
understand that this will cause all kinds of havoc with things like
ongoing TCP connections, and I accept that risk.
Check `man virsh` and the description to commands `snapshot-create-as`
and `snapshot-revert`. If more information is needed, feel free to ask,
although if deep knowledge is required I might need to rely on someone
else to reply then.
Have a nice day,
Martin
--
Gary Jackson
_______________________________________________
libvirt-users mailing list
libvirt-users(a)redhat.com
https://www.redhat.com/mailman/listinfo/libvirt-users
10:47 p.m.
On 9/19/2017 9:56 AM, Martin Kletzander wrote:
On Tue, Sep 19, 2017 at 01:28:45PM +0000, Jackson, Gary L. wrote:
>
> I would like to make a snapshot of a running VM, let it continue to run
> after the shapshot, and then at some later time roll back the VM to
> that previous running state. Can I do that with libvirt? If so, how? I
> understand that this will cause all kinds of havoc with things like
> ongoing TCP connections, and I accept that risk.
>
Check `man virsh` and the description to commands `snapshot-create-as`
and `snapshot-revert`. If more information is needed, feel free to ask,
although if deep knowledge is required I might need to rely on someone
else to reply then.
agreed. This is definitely achievable with snapshot-create-as. You'll
prefer to shutdown the VM to make it work, but it can be done live using
the --running flag. I've never tried this. The man page isnt entirely
clear but it seems like it will effectively reboot to the state when the
snapshot was taken.
Mechanics wise, you take the snapshot. Now you have a new disk image
file (usually with -snap, but you can name it whatever using
snapshot-as), that will be recording the changes that are happening to
the OS. The old image at the time of the snapshot is still there under
the original name. If you look in the xml file, you'll see it has
changed the path of the disk image to the new snapshot file. The new
snapshot is a 'sparse copy' in that is recording all of the new changes
happening, but it has a reference pointer pointing back to the original
image for things that have not changed. At any point, you can shut down
your VM and boot off the original image, which discards all of the
changes. Or you can decide that you want to 'blockcommit' all of the
changes back to the original image which you can do online without impact.
(I use this with ZFS replication to provide rollback capability per VM
image to another host in case of host failure)
11:17 p.m.
Will snapshot-revert restore the processor and memory state of the VM as it was at the
time of the snapshot?
--
Gary Jackson
On 9/19/17, 11:10 AM, "libvirt-users-bounces(a)redhat.com on behalf of Doug
Hughes" <libvirt-users-bounces(a)redhat.com on behalf of
doug.hughes(a)keystonenap.com> wrote:
On 9/19/2017 9:56 AM, Martin Kletzander wrote:
On Tue, Sep 19, 2017 at 01:28:45PM +0000, Jackson, Gary L. wrote:
>
> I would like to make a snapshot of a running VM, let it continue to run
> after the shapshot, and then at some later time roll back the VM to
> that previous running state. Can I do that with libvirt? If so, how? I
> understand that this will cause all kinds of havoc with things like
> ongoing TCP connections, and I accept that risk.
>
Check `man virsh` and the description to commands `snapshot-create-as`
and `snapshot-revert`. If more information is needed, feel free to ask,
although if deep knowledge is required I might need to rely on someone
else to reply then.
agreed. This is definitely achievable with snapshot-create-as. You'll
prefer to shutdown the VM to make it work, but it can be done live using
the --running flag. I've never tried this. The man page isnt entirely
clear but it seems like it will effectively reboot to the state when the
snapshot was taken.
Mechanics wise, you take the snapshot. Now you have a new disk image
file (usually with -snap, but you can name it whatever using
snapshot-as), that will be recording the changes that are happening to
the OS. The old image at the time of the snapshot is still there under
the original name. If you look in the xml file, you'll see it has
changed the path of the disk image to the new snapshot file. The new
snapshot is a 'sparse copy' in that is recording all of the new changes
happening, but it has a reference pointer pointing back to the original
image for things that have not changed. At any point, you can shut down
your VM and boot off the original image, which discards all of the
changes. Or you can decide that you want to 'blockcommit' all of the
changes back to the original image which you can do online without impact.
(I use this with ZFS replication to provide rollback capability per VM
image to another host in case of host failure)
11:25 p.m.
According to this page: https://wiki.libvirt.org/page/Snapshots
It saves complete memory state, or crash-consistent disk state, but not
both.
You probably want to test it thoroughly and see how it does. I only use
the disk-consistent snapshots.
On 9/19/2017 11:17 AM, Jackson, Gary L. wrote:
Will snapshot-revert restore the processor and memory state of the VM
as it was at the time of the snapshot?
--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)
12:53 a.m.
Thanks! The vanilla snapshot-create-as and revert commands work just exactly the way I’d
want them to. I’d gotten a bit confused by the documentation and went down a rabbit hole
with external snapshots.
Is there any way to make the snapshot and restore faster, like maybe by a decimal order of
magnitude? For example, will PXE booting the VM and running it entirely off of a RAM disk
and also using a RAM disk for the backing store help?
--
Gary Jackson
From: Doug Hughes <doug.hughes(a)keystonenap.com>
Date: Tuesday, September 19, 2017 at 11:25 AM
To: "Jackson, Gary L." <Gary.Jackson(a)jhuapl.edu>,
"libvirt-users(a)redhat.com" <libvirt-users(a)redhat.com>
Subject: Re: [libvirt-users] Rollback to running VM
According to this page: https://wiki.libvirt.org/page/Snapshots
It saves complete memory state, or crash-consistent disk state, but not both.
You probably want to test it thoroughly and see how it does. I only use the
disk-consistent snapshots.
On 9/19/2017 11:17 AM, Jackson, Gary L. wrote:
Will snapshot-revert restore the processor and memory state of the VM as it was at the
time of the snapshot?
--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)
[cid:image001.png@01D33146.522ABA40]
12:59 a.m.
I would estimate you are bounded by memory bandwidth (GB/sec - so not
much, but proportional to memory size) and disk bandwidth. So, using SSD
will help for certain vs spinning. I'm not sure about the catch-22
implicit with using a ramdisk, but since the ramdisk should be
previsioned from the host to the guest, it seems like it should work.
There may be other bottlenecks in drivers, etc. Not in my knowledge domain.
On 9/19/2017 12:53 PM, Jackson, Gary L. wrote:
Thanks! The vanilla snapshot-create-as and revert commands work just
exactly the way I’d want them to. I’d gotten a bit confused by the
documentation and went down a rabbit hole with external snapshots.
Is there any way to make the snapshot and restore faster, like maybe
by a decimal order of magnitude? For example, will PXE booting the VM
and running it entirely off of a RAM disk and also using a RAM disk
for the backing store help?
--
Gary Jackson
*From: *Doug Hughes <doug.hughes(a)keystonenap.com>
*Date: *Tuesday, September 19, 2017 at 11:25 AM
*To: *"Jackson, Gary L." <Gary.Jackson(a)jhuapl.edu>,
"libvirt-users(a)redhat.com" <libvirt-users(a)redhat.com>
*Subject: *Re: [libvirt-users] Rollback to running VM
According to this page: https://wiki.libvirt.org/page/Snapshots
<https://wiki.libvirt.org/page/Snapshots>
It saves complete memory state, or crash-consistent disk state, but
not both.
You probably want to test it thoroughly and see how it does. I only
use the disk-consistent snapshots.
On 9/19/2017 11:17 AM, Jackson, Gary L. wrote:
Will snapshot-revert restore the processor and memory state of the VM as it was at
the time of the snapshot?
--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)
--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)
5:20 a.m.
Putting the image on tmpfs cut the snapshot time down by quite a bit. It didn’t do much
for the restore time, probably because the images I’m using fit in the file cache
already.
Now I’m going to look in to profiling qemu to see where it’s spending all of its time.
--
Gary Jackson
From: Doug Hughes <doug.hughes(a)keystonenap.com>
Date: Tuesday, September 19, 2017 at 12:59 PM
To: "Jackson, Gary L." <Gary.Jackson(a)jhuapl.edu>,
"libvirt-users(a)redhat.com" <libvirt-users(a)redhat.com>
Subject: Re: [libvirt-users] Rollback to running VM
I would estimate you are bounded by memory bandwidth (GB/sec - so not much, but
proportional to memory size) and disk bandwidth. So, using SSD will help for certain vs
spinning. I'm not sure about the catch-22 implicit with using a ramdisk, but since the
ramdisk should be previsioned from the host to the guest, it seems like it should work.
There may be other bottlenecks in drivers, etc. Not in my knowledge domain.
On 9/19/2017 12:53 PM, Jackson, Gary L. wrote:
Thanks! The vanilla snapshot-create-as and revert commands work just exactly the way I’d
want them to. I’d gotten a bit confused by the documentation and went down a rabbit hole
with external snapshots.
Is there any way to make the snapshot and restore faster, like maybe by a decimal order of
magnitude? For example, will PXE booting the VM and running it entirely off of a RAM disk
and also using a RAM disk for the backing store help?
--
Gary Jackson
From: Doug Hughes
<doug.hughes@keystonenap.com><mailto:doug.hughes@keystonenap.com>
Date: Tuesday, September 19, 2017 at 11:25 AM
To: "Jackson, Gary L."
<Gary.Jackson@jhuapl.edu><mailto:Gary.Jackson@jhuapl.edu>,
"libvirt-users@redhat.com"<mailto:libvirt-users@redhat.com>
<libvirt-users@redhat.com><mailto:libvirt-users@redhat.com>
Subject: Re: [libvirt-users] Rollback to running VM
According to this page: https://wiki.libvirt.org/page/Snapshots
It saves complete memory state, or crash-consistent disk state, but not both.
You probably want to test it thoroughly and see how it does. I only use the
disk-consistent snapshots.
On 9/19/2017 11:17 AM, Jackson, Gary L. wrote:
Will snapshot-revert restore the processor and memory state of the VM as it was at the
time of the snapshot?
--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)
[cid:image001.png@01D33386.90476A70]
--
Doug Hughes
Keystone NAP
Fairless Hills, PA
1.844.KEYBLOCK (539.2562)
[cid:image002.png@01D33386.90476A70]
2538
days inactive
2545
days old
7 comments
3 participants
participants (3)
-
Doug Hughes -
Jackson, Gary L. -
Martin Kletzander