10:45 a.m.
Hello,
I'd like to live migration with snapshots.
But it doesn't work. It comes out a message "cannot migrate domain with 1
snapshots"
Then I try to trace the code(Libvirt 0.9.8 to 1.0.3), I find out the code
in src/qemu/qemu_migration.c @ Line 1395 - 1440 (Libvirt 1.0.3)
It will check the VM which has snapshots or not.
I just curious about this limitation, why the VM can't live migration with
snapshots?
What happen if I skip this check?
Does it has any suggestion way or virsh command with options to do live
migration with snapshots?
Thanks a lot.
Hubert
11:40 a.m.
On 03/20/2013 08:45 PM, Chiang Hubert wrote:
Hello,
I'd like to live migration with snapshots.
But it doesn't work. It comes out a message "cannot migrate domain with 1
snapshots"
Unfortunately, figuring out how to migrate snapshot information at the
libvirt API level requires some engineering work - the current RPC
protocol for migration is not set up to migrate an arbitrary amount of
snapshots in a single call.
On the other hand, if you are allowed to make more than one API call,
the solution is already available; maybe we should patch virsh to learn
how to make the series of API calls, to automate what I will describe below.
Then I try to trace the code(Libvirt 0.9.8 to 1.0.3), I find out the code
in src/qemu/qemu_migration.c @ Line 1395 - 1440 (Libvirt 1.0.3)
It's still unimplemented at the libvirt level, even in libvirt.git.
It will check the VM which has snapshots or not.
I just curious about this limitation, why the VM can't live migration with
snapshots?
Doing it all in one RPC call would be a potential denial-of-service
(RPCs are bounded in length to avoid consuming server resources, and
taking lots of snapshots on the source could easily be made to exceed
bounds). If someone can design a way to set up a series of RPC
handshakes, then we could do it at the libvirt level in a single API
call, but I'm not sure it is worth it.
What happen if I skip this check?
Does it has any suggestion way or virsh command with options to do live
migration with snapshots?
The existing solution at the management tool layer is to migrate the
snapshot information first, and then to migrate the domain. For each
snapshot in 'virsh snapshot-list --name $dom', you will want to 'virsh
snapshot-dumpxml $dom $name > file' on the source, then 'virsh
snapshot-create --redefine $dom file' on the destination. Next,
determine 'virsh snapshot-current --name $dom' on the source, and use
'virsh snapshot-current $dom $name' on the destination to set it as
current (if there is a current snapshot). After the destination has all
the snapshots, you then loop over 'virsh snapshot-delete --metadata $dom
$name' on the source, at which point, live migration will now work.
Patches to teach virsh how to do all this work in a single 'virsh
migrate' are welcome.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
2:39 p.m.
Dear Eric,
Thanks for your tips and explanations.
I think there will be lots of works to do.
And I migrate VM with snapshot successfully by your tips.
Thank you so much. I am really appreciated.
Hubert
On Thu, Mar 21, 2013 at 11:40 AM, Eric Blake <eblake(a)redhat.com> wrote:
On 03/20/2013 08:45 PM, Chiang Hubert wrote:
> Hello,
>
> I'd like to live migration with snapshots.
>
> But it doesn't work. It comes out a message "cannot migrate domain with 1
> snapshots"
Unfortunately, figuring out how to migrate snapshot information at the
libvirt API level requires some engineering work - the current RPC
protocol for migration is not set up to migrate an arbitrary amount of
snapshots in a single call.
On the other hand, if you are allowed to make more than one API call,
the solution is already available; maybe we should patch virsh to learn
how to make the series of API calls, to automate what I will describe
below.
>
> Then I try to trace the code(Libvirt 0.9.8 to 1.0.3), I find out the code
> in src/qemu/qemu_migration.c @ Line 1395 - 1440 (Libvirt 1.0.3)
It's still unimplemented at the libvirt level, even in libvirt.git.
>
> It will check the VM which has snapshots or not.
>
> I just curious about this limitation, why the VM can't live migration
with
> snapshots?
Doing it all in one RPC call would be a potential denial-of-service
(RPCs are bounded in length to avoid consuming server resources, and
taking lots of snapshots on the source could easily be made to exceed
bounds). If someone can design a way to set up a series of RPC
handshakes, then we could do it at the libvirt level in a single API
call, but I'm not sure it is worth it.
>
> What happen if I skip this check?
>
> Does it has any suggestion way or virsh command with options to do live
> migration with snapshots?
The existing solution at the management tool layer is to migrate the
snapshot information first, and then to migrate the domain. For each
snapshot in 'virsh snapshot-list --name $dom', you will want to 'virsh
snapshot-dumpxml $dom $name > file' on the source, then 'virsh
snapshot-create --redefine $dom file' on the destination. Next,
determine 'virsh snapshot-current --name $dom' on the source, and use
'virsh snapshot-current $dom $name' on the destination to set it as
current (if there is a current snapshot). After the destination has all
the snapshots, you then loop over 'virsh snapshot-delete --metadata $dom
$name' on the source, at which point, live migration will now work.
Patches to teach virsh how to do all this work in a single 'virsh
migrate' are welcome.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
4245
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2 comments
3 participants
participants (3)
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Chiang Hubert -
Eric Blake -
Hubert Chiang