[libvirt-users] Using virsh blockcopy -- what's it supposed to accomplish?

[Paolo Bonzini]

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On 08/01/2015 22:04, Eric Blake wrote:
> Where are you specifying the format?  I have not personally played
>  with NBD much.  But here's my guess: Even though 
> /tmp/dsk.test.qcow2 is a qcow2 file, the NBD server is serving up a
> RAW image through /dev/nbd2. Thus, if you are trying to treat 
> /dev/nbd2 as the destination of your copy, you MUST tell qemu that
>  the file format of the copy is to be raw (regardless of the file 
> format of the original that is being copied from).  If you omit the
> --raw (also spelled --format=raw in newer libvirt) parameter to the
> virsh blockcopy command, then libvirt has to guess at the 
> destination format; if the source was qcow2, then libvirt will 
> guess that the destination should be qcow2 as well.  But writing 
> qcow2 data to a raw NBD disk means you have created a nested file 
> in /tmp/dsk.test.qcow2 - it is a qcow2 file whose contents are a 
> qcow2 file whose contents are the raw data (not typical usage, and
>  a bit weird to wrap your head around).

I think you're right.

Paolo
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