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Re: [libvirt] [PATCH] support sheepdog volumes

On Wed, Nov 17, 2010 at 06:19:58PM +0900, MORITA Kazutaka wrote:
> Sheepdog is a distributed storage system for QEMU. It provides highly
> available block level storage volumes to VMs like Amazon EBS.  This
> patch adds support for Sheepdog; we can create VMs with sheepdog
> volumes, and attach sheepdog volumes to running machines via the
> attach-device command.
> Sheepdog volumes can be declared like this:
>     <disk type='sheepdog' device='disk'>
>       <driver name='qemu' type='raw' />
>       <source vdi='volume_name' host='hostname' port='7000'/>
>       <target dev='vda' bus='virtio' />
>     </disk>
> 'host' and 'port' in the source element are optional.  If they are not
> specified, sheepdog clients use the default value (localhost:7000).

I'm not too familiar with sheepdog implementation, but I understand
that each block device is stored across multiple hosts, but you're
only listing one hostname here.  In the proposal for supporting RBD/
CEPH in libvirt/QEMU, there's tan option to give multiple hostnames. 
Is the need to give multiple hostnames going to be something that
is also relevant for Sheepdog, or does it cope with this in an
entirely different way ?

As mentioned in the RBD thread[1], I'm wondering whether we should aim
for separate 'types' for each network block device or try to merge
them into one common syntax like

     <disk type="network" device="disk">
       <driver name="qemu" type="raw" />
       <source protocol='rbd|sheepdog|nbd' name="...some image identifier...">
         <host name="mon1.example.org" port="6000">
         <host name="mon2.example.org" port="6000">
         <host name="mon3.example.org" port="6000">
       <target dev="vda" bus="virtio" />


[1] http://www.redhat.com/archives/libvir-list/2010-November/msg00847.html
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