Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description

[Paolo Bonzini]

On 21/04/2015 03:25, Wen Congyang wrote:
>> > Please do not introduce "<name>+colo" block drivers.  This approach is
>> > invasive and makes block replication specific to only a few block
>> > drivers, e.g. NBD or qcow2.
> NBD is used to connect to secondary qemu, so it must be used. But the primary
> qemu uses quorum, so the primary disk can be any format.
> The secondary disk is nbd target, and it can also be any format. The cache
> disk(active disk/hidden disk) is an empty disk, and it is created before run
> COLO. The cache disk format is qcow2 now. In theory, it can be ant format 
> which
> supports backing file. But the driver should be updated to support colo mode.
> 
> > A cleaner approach is a QMP command or -drive options that work for any
> > BlockDriverState.
> 
> OK, I will add a new drive option to avoid use "<name>+colo".

Actually I liked the "foo+colo" names.

These are just internal details of the implementations and the
primary/secondary disks actually can be any format.

Stefan, what was your worry with the +colo block drivers?

Paolo