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

[Keith Busch <kbusch@kernel.org>]

On Fri, May 01, 2026 at 08:47:35PM +0100, Matthew Wilcox wrote:
> 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.

Maybe I'm out of touch with reality, but I could swear active-passive
setups are often configured such that the passive node for one resource
is the active node for another. That would also suffer the same link
capacity issues you're describing.