Re: [Lsf-pc] [LSF/MM/BPF TOPIC] A block level, active-active replication solution

[Matthew Wilcox <willy@infradead.org>]

On Tue, Feb 03, 2026 at 04:09:59PM +0100, Haris Iqbal via Lsf-pc wrote:
> We are working on a pair of kernel modules which would offer a new
> replication solution in the Linux kernel. It would be a block level,
> active-active replication solution for RDMA transport.

Why is active-active a good idea?

With an active-passive solution, network traffic is directed to the
active node.  Over time at some point we get close to saturating the
link and performance drops.  At that point, human intervention will
occur and the network link will be upgraded.

With an active-active solution, traffic goes to each node.  At smoe point
each link will be about 75% utilised and we won't see any performance
problems.  But then a node goes down and all of a sudden the remaining
node is being hit with 150% of the link capacity.  There's no gradual
degradation here; the whole solution just goes down.

Of course it doesn't have to be network capacity either; it could be CPU,
RAM or any other resource needed to service the requests.

Active-active is fragile and I would never recommend such a solution.
I won't be in your session, but I thought it worth raising this point.