True memory-synchronous write flushing — drbd protocol B-?

Question

Is there a way in DRBD to make a real fully memory-synchronous cache? I might best explain substituting current explanation with my own one:

Protocol B. Memory synchronous (semi-synchronous) replication protocol. Local write operations on the primary node are considered completed as soon as the local disk write has occurred, and the replication packet has reached the peer node.

What I am looking for is:

Protocol B-. Memory synchronous (semi-synchronous) replication protocol. Local write operations on the primary node are considered completed as soon as they are in local write cache, and the replication packet has reached the peer node.

Maybe possible with something else than DRBD? Network is 10G, plenty of RAM.

Answer 1

Sure you can do this in DRBD, just write your own protocol handler. There is no way to do this with the current range of protocols available. Get a decent battery-backed RAID controller and you can get the same performance, though, without the risk.