[Gluster-devel] Multicast Support?

[Gordan Bobic]

On Tue, 10 Feb 2009 15:56:21 +0530, Anand Avati <avati at zresearch.com>
wrote:
>> One other thing occurs to me - in cases where multicast isn't directly
>> available, an externel helper/replicator would be equally useful for
>> emulating a similar thing.
>>
>> For example, if I have 4 systems on 2Mb pipes (e.g. DSL) and have a
>> system
>> at a colo on a cheal all-I-can-eat 10Mb pipe, it would make sense for
>> each
>> machine to send it's writes ONLY to the colo-ed machine, which can then
>> replicate the write to the 3 other systems. This means that systems on
>> 2Mb
>> pipes would still get 2Mb if write bandwidth. In the classic setup, they
>> would only get (2/3)Mb of write bandwidth.
>>
>> I've been thinking about setting this up as 4 separate AFRs (each
between
>> one satellite node and the central node), but I am not sure whether
>> writes
>> would actually propagate. Can any of the devs hazard a guess as to what
>> would happen? Would locking still work if each of the satellite nodes
>> specifies the core replication node in it's AFR node list? The one
>> problem
>> with this that I can see is that the core node would also have to
contain
>> all the data - I cannot think of a way around this at the moment.
>>
>> Has anyone got any thoughts on this?
> 
> GlusterFS relies upon the transport being reliable. Using multicast
> for reliable transfers is quite tricky and would need considerable
> redesign of the current codebase atleast.

What about using an external high-bandwidth helper/hub node to do the
(inverse) multiplexing for writes? This wouldn't require using UDP
multicast.

Gordan