Using ZFS in a Postgres VM?

Prox marks wants you to use ZVals, which frequently don't perform as well as raw files or QCal 2 files. And it uses 8K as the vol block size. The bigger problem of the two is going to depend on your workload,. It's probably not going to be appropriate for most other workloads because what you might potentially gain in lower latency on small I.O., you're going to lose very rapidly and amplify when you need to do larger file operations.