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
