Yes you can have all or a bunch of these features like failure domains via other routes/products but none have all of the stuff together in one place like CEPH.
There's a reason people call it the "Linux of storage". The only alternatives are manage this at a higher level in your stack (reinventing the wheel) or buying PB level solutions from corporate which is like saying I'm buying Oracle and MS over Linux.
Protocol replication means you've reimplemented something which is storage related elsewhere in your stack. It's not incorrect to do so, but there exist better solutions and alternatives now.
Most of all, it's doing split brain recovery; which - if we wanted CP rather than AP then we wouldn't need, but that wasn't the original design.
If I was redoing this from scratch, I'd maybe do Ceph or similar and update Cyrus to work well with it, but that would be a big change from the current design.
Anyway, I'm happy to stipulate that Ceph is great tech, without going and telling other people that it's the only choice.
Split brain stuff only happens when you're splitting a single threaded task and put it back together. MDS in CEPH has this problem but that's so far into the weeds here as to be off topic.
Again you're implementing something storage not in storage and taking any storage. Fine if you want to do it that way, but talk about _that_ not hecking ZFS being mah saviour. (Btw daily driving and love that too but an email provider _relying_ on it should raise eye brows)...
