Re: [Qemu-devel] [PATCH] This patch adds a new block driver : iSCSI

[Paolo Bonzini]

On 09/15/2011 01:42 PM, Dor Laor wrote:
> > However, iSCSI is a complex protocol and a complex suite of tools. With
> > a simpler set of tools such as qemu-nbd/nbd, you can for example tunnel
> > data over the libvirt connection. Possibly with encryption. Also, with
> > iSCSI you're tied to raw, while qemu-nbd lets you use qcow2.
>
> My main motivation for external iScsi is to provide qemu operations w/
> non shared storage. Things like streaming an image w/o shared storage or
> block live migration can be done where the src host exposes iscsi target
> and the destination is the initiator. In case of qcow2, every snapshot
> in the chain should be exposed as a separate LUN. The idea is to ignore
> the data in the guest image and treat it as opaque.

Then you need an iSCSI *target* that understands qcow2, like qemu-nbd 
but for iSCSI... that's exactly the thing you were worried about 
implementing.

(Of course you could use qemu-nbd and expose /dev/nbd* via iSCSI, but it 
starts looking like an exercise in adding layers of indirections! :)).

Paolo