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[Qemu-devel] Re: [kvm-devel] Feedback and errors
From: |
Daniel P. Berrange |
Subject: |
[Qemu-devel] Re: [kvm-devel] Feedback and errors |
Date: |
Fri, 2 May 2008 15:45:27 +0100 |
User-agent: |
Mutt/1.4.1i |
On Fri, May 02, 2008 at 01:52:18PM +0300, Avi Kivity wrote:
> nadim khemir wrote:
> > Hi, great work.
> >
> > While playing with kvm-qemu I noticed a few points that might be of
> > interrest:
> >
> > 1/ -loadvm and -snapshot don't work together. It works as if -loadvm wasn't
> > passed as argument
> >
> > 2/ two instances of kvm can be passed the same -hda. There is no locking
> > whatsoever. This messes up things seriously.
That depends entirely on what you are doing with the disk in the guest OS.
The disk could be hosting a cluster filesystem. The guest OS could be
running on a read-only root FS. The disk could be application raw data
storage which can be shared (eg Oracle RAC).
And if the disk is backed by a physical volume which is accessible to
multiple hosts, locking on the VM's host won't provide any safety against
VMs on another host accessing it.
> These two are upstream qemu problems. Copying qemu-devel.
>
> I guess using file locking by default would improve the situation, and
> we can add a -drive ...,exclusive=no option for people playing with
> cluster filesystems.
Turning on file locking by default will break existing apps / deployments
using shared disks. IMHO this is a policy decision that should be solved
at ahigher level in the management stack where a whole world view is
available rather than QEMU which only knows about its own VM & host.
Dan.
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[Qemu-devel] Re: [kvm-devel] Feedback and errors,
Daniel P. Berrange <=