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

[Paolo Bonzini]

On 23/04/2015 14:05, Dr. David Alan Gilbert wrote:
> As presented at the moment, I don't see there's any dynamic reconfiguration
> on the primary side at the moment

So that means the bdrv_start_replication and bdrv_stop_replication
callbacks are more or less redundant, at least on the primary?

In fact, who calls them?  Certainly nothing in this patch set...
:)

Paolo

 - it starts up in the configuration with
> the quorum(disk, NBD), and that's the way it stays throughout the 
> fault-tolerant
> setup; the primary doesn't start running until the secondary is connected.
> 
> Similarly the secondary startups in the configuration and stays that way;
> the interesting question to me is what happens after a failure.
> 
> If the secondary fails, then your primary is still quorum(disk, NBD) but
> the NBD side is dead - so I don't think you need to do anything there
> immediately.
> 
> If the primary fails, and the secondary takes over, then a lot of the
> stuff on the secondary now becomes redundent; does that stay the same
> and just operate in some form of passthrough - or does it need to
> change configuration?
> 
> The hard part to me is how to bring it back into fault-tolerance now;
> after a primary failure, the secondary now needs to morph into something
> like a primary, and somehow you need to bring up a new secondary
> and get that new secondary an image of the primaries current disk.