Re: [Libguestfs] [PATCH v4 0/3] v2v: Add -o rhv-upload output mode.

On 03/08/2018 06:29 AM, Richard W.M. Jones wrote: >NBD (the protocol) doesn't "know" about qcow2 files. You can serve >any file you want as a range of bytes, including qcow2, but that >requires whatever is consuming those bytes to then do the qcow2 >en-/decoding. (Which means effectively the client has to be qemu >because nothing else can parse qcow2 reliably). In the qemu-img >convert case above this all works because qemu-img (ie. qemu) is the >client, and it does the encoding of qcow2, and we're just shuffling a >byte stream to oVirt imageio. One caveat: NBD cannot (yet) resize disks (there is a proposal to implement a new command that would optionally allow an NBD client to request a resize, and/or a server to advertise an updated size back to the client beyond the initial size learned at connect, but that proposal still needs ironing out and an initial implementation). As such, if you are serving a qcow2 file as raw bytes over NBD, you MUST be sure that the NBD server already has a sufficient size for the file it is serving, because the client interpreting qcow2 will not be able to do anything if its qcow2 usage patterns require more space than the NBD server already advertised.