Explain why people should be using the "raw" image format for RBD
volumes created for use by QEMU: using any other format adds only
overhead, but no extra value (since RBDs are also CoW and
thin-provisioned), plus the Qcow2 storage driver is not migration safe
when caching is enabled, whereas the RBD driver is.
Also, fix a minor glitch in the example qemu-img commands ("-f rbd"
and "-O rbd" should really be "-f raw" and "-O raw").
Finally, drop the "-f" option altogether on qemu-img commands where it
makes no sense (info and resize).
Signed-off-by: Florian Haas <florian@hastexo.com>
