libvirt users - May 2010 - Can not restore domain from a shared state file

Hi,

I have two KVM host: h1 and h2, both of them mount an NFS directory as a
shared storage.
I can save (virsh save <domain> <file>) a domain in h1 to a state
file in
the shared storage successfully, but failed to restore it from h2 with the
following error message:
# virsh restore testRes.dat
error: Failed to restore domain from testRes.dat
error: operation failed: failed to start VM

I can always restore it from h1, but sometimes works for h2 (wait for a
while, then "virsh restore" command may succeed in h2). I guess the
state
file generated by "virsh save" command is not intact from h2 point
view, may
be cause by the cache of NFS server?

Any suggestions will be really appreciated, thanks in advance!


Regards,
Qian
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://listman.redhat.com/archives/libvirt-users/attachments/20100511/a4eaa289/attachment.htm>

I found that waiting for a while does not work, but if I tried to restore it
from h2 more times, it will work.
For example, if I save a domain which has 512MB memory, and restore if from
h2 repeatedly, at the third time, the restore can succeed, but  for a 256MB
domain, it will succeed at the second time.


2010/5/11 Zhang Qian <zhq527725 at gmail.com>
> Hi,
>
> I have two KVM host: h1 and h2, both of them mount an NFS directory as a
> shared storage.
> I can save (virsh save <domain> <file>) a domain in h1 to a
state file in
> the shared storage successfully, but failed to restore it from h2 with the
> following error message:
> # virsh restore testRes.dat
> error: Failed to restore domain from testRes.dat
> error: operation failed: failed to start VM
>
> I can always restore it from h1, but sometimes works for h2 (wait for a
> while, then "virsh restore" command may succeed in h2). I guess
the state
> file generated by "virsh save" command is not intact from h2
point view, may
> be cause by the cache of NFS server?
>
> Any suggestions will be really appreciated, thanks in advance!
>
>
> Regards,
> Qian
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://listman.redhat.com/archives/libvirt-users/attachments/20100511/d5ef848f/attachment.htm>

On 05/11/2010 04:40 AM, Zhang Qian wrote:
> Hi,
>
> I have two KVM host: h1 and h2, both of them mount an NFS directory as 
> a shared storage.
> I can save (virsh save <domain> <file>) a domain in h1 to a
state file
> in the shared storage successfully, but failed to restore it from h2 
> with the following error message:
> # virsh restore testRes.dat
> error: Failed to restore domain from testRes.dat
> error: operation failed: failed to start VM
>
> I can always restore it from h1, but sometimes works for h2 (wait for 
> a while, then "virsh restore" command may succeed in h2). I guess
the
> state file generated by "virsh save" command is not intact from
h2
> point view, may be cause by the cache of NFS server?
There is a race condition in qemu when restarting a domain - it is 
possible for qemu to start the CPU before the domain image has been read 
from the file (this is regardless of where the file is stored). This may 
or may not be your problem (the error condition I saw due to this race 
was different from what you are seeing). It is easy to test for though - 
before saving your domain, first suspend it with "virsh suspend 
<domain>", then save it; after you've restored the domain with
"virsh
restore <image-file>", resume the domain with "virsh resume
<domain>".
If the domain successfully resumes, your problem was the race I 
describe. If not, you have found a different problem.

I'm interested to know if this solves your problem.