Github user andytaylor commented on the issue:
https://github.com/apache/activemq-artemis/pull/1747
There is no point in waiting until its written to disc, it just adds extra
latency and gives you no extra guarantees. If the backup crashes when the live
is still up then it would start replicating from scratch again anyway. If it
crashes during the window after the live has crashed but before the backup has
finished synching then you have lost HA anyway, however you still have data
integrity at the original live broker
---