Re: [Qemu-devel] Design of the blobstore

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Sep 15, 2011 at 12:17:54PM +0100, Stefan Hajnoczi wrote:
> On Wed, Sep 14, 2011 at 6:05 PM, Stefan Berger
> <stefanb@linux.vnet.ibm.com> wrote:
> >  One property of the blobstore is that it has a certain required size for
> > accommodating all blobs of device that want to store their blobs onto. The
> > assumption is that the size of these blobs is know a-priori to the writer of
> > the device code and all devices can register their space requirements with
> > the blobstore during device initialization. Then gathering all the
> > registered blobs' sizes plus knowing the overhead of the layout of the data
> > on the disk lets QEMU calculate the total required (minimum) size that the
> > image has to have to accommodate all blobs in a particular blobstore.
> 
> Libraries like tdb or gdbm come to mind.  We should be careful not to
> reinvent cpio/tar or FAT :).

qcow2 is desirable because it lets us provide encryption of the blobstore
which is important if you don't trust the admin of the NFS server, or the
network between the virt host & NFS server.

> What about live migration?  If each VM has a LUN assigned on a SAN
> then these qcow2 files add a new requirement for a shared file system.

NB, I'm not neccessarily recommending this, but it is possible to
format a raw block device, to contain a qcow2 image. So it does not
actually require a shared filesystem. it would however require an
additional LUN, or require that the existing LUN be partitioned into
two parts.


Daniel
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