On 09/11/2010 11:53 AM, Stefan Hajnoczi wrote:
On Sat, Sep 11, 2010 at 3:04 PM, Anthony Liguori<aligu...@us.ibm.com> wrote:
Additionally, there's a spurious read when using an nbd protocol that can be
quite destructive when using copy-on-read. Potentially, this can lead to
probing an image file over top of NBD but this is completely wrong as NBD
devices are not growable.
Can you describe the copy-on-read scenario where the 2 KB probe read
is a problem?
Accessing a fixed size image file over NBD is probably uncommon, but
I'm not sure if there's a reason to forbid it.
I think the better solution is to explicitly specific raw with nbd.
IOW, I think -drive file=nbd:localhost:1026,format=raw should work the
same way. I still feel slightly weird about probing happening with
nbd. It seems like it could only result in badness.
The specific scenario is migration. I'm using a copy-on-read file on
the destination and I want to be sure that I don't read any blocks
(since they're copied) until the source stops execution.
Regards,
Anthony Liguori
Stefan
