64K is generally small recordsize. For media they recommend 1M. My db was sitting on the default 128K recordsize and perforned fine on 10.10. It doesn’t matter much for reads because ZFS keeps it in RAM and if it gets evicted it goes into SSD cache (l2arc). But for writes the cache wouldn’t help unless I disable sync which risks data loss. I don’t think 10.10 did much writes during lib scan so write perf only mattered when something changed.