Il 09/08/2012 14:52, ronnie sahlberg ha scritto: >> > >> > guest uses noop right now. Disk Host is nexentastor running open solaris. I >> > use libiscsi right now so the disks are not visible in both cases >> > (virtio-blk and virtio-scsi) to the host right now. >> > > And if you mount the disks locally on the host using open-iscsi, and > access them as /dev/sg* from qemu, what performance do you get?
Good question. > virtio-blk would first go to scsi emulation and then call out to > block/iscsi.c to translate back to scsi commands to send to libiscsi > > while virtio-scsi (I think) would treat libiscsi as a generic scsi > passthrough device. I.e. all commands just go straight through > bdrv_aio_ioctl(SG_IO) I think he's not using scsi-block or scsi-generic, because 1.0 libiscsi didn't support that. scsi-generic would indeed incur some overhead because it does not do scatter/gather I/O directly, but scsi-hd/scsi-block do not have this overhead. In any case, that should be visible through the output of perf if it is significant. Paolo
