[DRBD-user] drbd & multicast?

[Volodymyr Litovka]

Hi,

On 04.04.2020 14:16, Volodymyr Litovka wrote:

> while for more scaled systems, where most of VMs will reside on
> diskless nodes, this will have a notable performance impact

For example, in Openstack, where Nova knows nothing about Cinder's
volumes placement, there are no ways (at least - simple) to reside VM on
same node with volume. So, e.g. in the project with 5+ nodes and two
replicas, probability of residing VM on "diskless" node becomes very high.

> The question is - whether DRBD supports multicast in order to generate a
> single flow from originating node? This will allow to dramatically
> improve performance of scaled system and will allow to build more scaled
> systems.

This change however, can significantly impact the source code and will
require much efforts.

To avoid this, I'd propose to add additional layer like proxy, which will:

- reside on every satellite
- receive data over unicast
** thus, drbd code will get minimal changes (now - it sends unicast data
to 1+ neighbors, after changes - it will send the same unicast to single
neighbor)
** to minimize delay - use local sockets
- resend it over multicast
- but manage control traffic (e.g. acknowledgments from remote peers)
over unicast

Thank you.


--
Volodymyr Litovka
   "Vision without Execution is Hallucination." -- Thomas Edison