I can tell you this; it’s not ZFS or it’s quotas. I know that Postgres has no problems with ZFS and quotas; I have seen Postgres development environments run out of quota space on ZFS and Postgres never got corrupted — it would just crash and end up in a crash/restore loop. Just increase the quota and Postgres recovers without issue exiting the crash/restore loop, cleanup the rouge space usage, and reduce the quota back down. It makes recovering from out of space issues very quick.