[libvirt] Local storage-migration plus network disks (Ceph RBD)

Hi there, We have a production OpenStack cloud, currently on Qemu 1.0 & 1.5 with Libivrt 1.1.1. We're using local storage with storage-migration when we need to move machines around. Since we built this thing we've noticed that with network storage attached (have seen this with iSCSI and Ceph RBD targets, mainly interested in the latter) the migration moves all of the network disk contents as well, which for any non-toy disk sizes pretty much renders it useless as the migration is then bounded not by the guest memory size and activity but also by the block storage size. E.g., an idle guest with 8GB RAM and a 300GB Ceph RBD attached takes ~3 hours to migrate (over a 20GE network) and we observe balanced TX/RX on both the source and destination, as the source reads blocks from the Ceph cluster, streams them to the destination, and the destination in turn writes them back to the Ceph cluster. Looking in Libvirt's qemu_migration.c code I see qemuMigrationDriveMirror skips shared, RO and source-less disks. But I'm not sure why network disks in general, and in particular RBDs, wouldn't be considered shared for these purposes. From my naive reading the checks in qemuMigrationIsSafe (which explicitly pass NETWORK+RBD) seem to confirm this, at least for RBDs. Is this a bug? -- Cheers, ~Blairo