Re: [Libguestfs] [Qemu-block] v2v: -o rhv-upload: Long time spent zeroing the disk

On 04/12/2018 05:24 AM, Richard W.M. Jones wrote: > I don't think we have nbd-server in RHEL, and in any case wouldn't it > be better to use qemu-nbd? > > You just start a new qemu-nbd process instead of faffing around with > configuration files, kill the qemu-nbd process when you're done, and

qemu-nbd supports qcow2 already.

That, and qemu-nbd supports extensions such as NBD_CMD_BLOCK_STATUS and NBD_OPT_STRUCTURED_REPLY that nbd-server has not implemented yet; a qemu NBD client talking to a qemu-nbd server is thus going to be able to take advantage of those extensions for better performance that would not be possible with a qemu NBD client talking to an nbd-server instance (at least, not without someone implementing the new features there). And this is no different from the situation where nbdkit as the server lacks several features; the current rhv-upload patches use a python plugin to nbdkit, which is implemented as serializing all requests; while using qemu-nbd as the server would allow parallel requests to be in flight simultaneously.