The Saturday 30 Aug 2014 à 17:02:12 (+0100), Richard W.M. Jones wrote : > On Sat, Aug 30, 2014 at 05:53:43PM +0200, Benoît Canet wrote: > > The Saturday 30 Aug 2014 à 15:46:41 (+0100), Richard W.M. Jones wrote : > > > For the benefit of those who have absolutely no idea what you're > > > talking about, could you write a simpler summary of what you're trying > > > to do? > > > > > > Rich. > > > > Hello, > > > > Most cloud providers sell virtualized instances either using Xen or KVM. > > > > However another trend is to provide bare metal instances for people > > who want the highest CPU and network performance possible.(typicaly > > people doing computation with MPI) > > > > So a cloud end user would need to be able to instanciate a virtual > > machine use it for a while then stop the virtual machine, change the > > hardware type to bare metal and restart the instance while keeping > > using the same boot volume. > > > > QEMU will keep a virtual machine data stored in one of it's numerous > > storage backend format like QCOW2 or QED. > > > > If the cloud provider want to be able to boot QCOW2 or QED images on > > bare metal machines he will need to export QCOW2 or QED images on > > the network. > > > > So far only qemu-nbd allows to do this and it is neither well > > performing nor really convenient to boot on a bare metal machine. > > So I think what you want is a `qemu-iscsi'? ie. the same as qemu-nbd, > but with an iSCSI frontend (to replace the NBD server). > > I think this is an excellent idea, although AIUI iSCSI is a pretty > complex protocol. (I wrote an NBD server, and the protocol is almost > trivial, albeit as you say, performing badly). > > > So summarize I am looking for a way to export QCOW2 or QED image as > > an ISCSI or FCOE targets while keeping all the goodies these format > > provides (taking snapshots for backup, streaming, mirroring). > > > > Reusing LIO code would help tremendously to simplify this task. > > I guess so. Are you planning to integrate bits of LIO into qemu, or > bits of qemu into LIO? > > The latter has been tried various times, without much success. See > the many examples of people trying to make the qemu block driver code > into a separate library, and failing.
Paolo pointed me to Andy's current work so I started this discution: http://thread.gmane.org/gmane.linux.kernel/1771465. I know well enough the QEMU block layer to be aware that it's riddled with static variables so I think bits of Andy's current work on top of a qemu-lio command would be the way. >> Writing an iSCSI front end to qemu would be good, but qemu has some > very particular policies about what code can be introduced, so that > could be tricky too ... Where can I read these policies ? Best regards Benoît > > Rich. > > -- > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones > Read my programming and virtualization blog: http://rwmj.wordpress.com > libguestfs lets you edit virtual machines. Supports shell scripting, > bindings from many languages. http://libguestfs.org
