Re: Sharing disks between two kvm guests

[Laurent Vivier <Laurent.Vivier@bull.net>]

Le vendredi 20 juin 2008 à 11:37 -0500, Anthony Liguori a écrit :
> Laurent Vivier wrote:
> > Le vendredi 20 juin 2008 à 09:07 -0500, Javier Guerra a écrit :
> >   
> >> On Fri, Jun 20, 2008 at 7:23 AM, carlopmart <carlopmart@gmail.com> wrote:
> >>     
> >>> Felix Leimbach wrote:
> >>>       
> >>>>>  This is my first post to this list. I have already installed kvm-70
> >>>>> under rhel5.2. My intention is to share on disk image betwwen two rhel5.2
> >>>>> kvm guests. Is it possible to accomplish this in kvm like xen or vmware
> >>>>> does?? How can I do?? I didn't find any reference abou this on kvm
> >>>>> documentation ...
> >>>>>           
> >> i tried this looong ago and didn't really work because there was some
> >> userspace cache on each QEMU instance.  but the -drive option has a
> >> 'cache=off' setting that should be enough.
> >>
> >> in theory (i haven't tested, but Avi 'blessed' it):
> >> - create a new image with qemu-img
> >> - add it to the command line using -drive file=xxx,cache=off on both
> >> KVM instances
> >> - use a cluster filesystem!
> >>     
> >
> > RFC:
> >
> > Well, well, perhaps it is delusions of a sick mind but since the
> > introduction of qemu-nbd I think we can develop easily something to
> > share a disk between several virtual hosts:
> >
> > I- in a first step, we can modify qemu-nbd to accept several connections
> > for one disk image, for instance:
> >
> > # qemu-nbd my-disk.qcow2
> > # nbd-client localhost 1024 /dev/nbd0
> > # nbd-client localhost 1024 /dev/nbd1
> >
> > and start two virtual hosts:
> >
> > "qemu -hda v1.img -hdb /dev/nbd0" and "qemu -hda v2.img -hdb /dev/nbd1"
> >
> > Of course the filesystem must know how to share the access to the disk
> > with others (-> "cluster filesystem")
> >
> > II- in a second step, we can include directly the nbd protocol in qemu
> > (block-nbd.c, "-drive file=nbd:localhost:1024") to connect to the
> > server. We can also add some commands to the protocol to manage lock,
> > HA, "what else ?" (Hi George).
> >   
> 
> http://hg.codemonkey.ws/qemu-pq/file/25ca451f2040/block-nbd.diff

You're not fun, Anthony.

Perhaps, now, it should be better if you use functions defined in the
(new) file "nbd.c".

Laurent

> Regards,
> 
> Anthony Liguori
> 
> > Any comments ?
> >
> > Cheers,
> > Laurent
> >   
> 
> 
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