Is the ZVOL 8 kB block size the most performant option (iSCSI+ZFS) with a VMFS-5 volume?
VMFS-5 datastores use a 1MB block size and 8kB sized sub-blocks, so the default 8 kB block looks like a pretty reasonable and logical option to increase IOPS (while probably sacrificing a little bit the total data burst) but I haven't seen accurate comparative tests so far with bigger blocks (64 kB, for example) and Freenas
VMFS-5 datastores use a 1MB block size and 8kB sized sub-blocks, so the default 8 kB block looks like a pretty reasonable and logical option to increase IOPS (while probably sacrificing a little bit the total data burst) but I haven't seen accurate comparative tests so far with bigger blocks (64 kB, for example) and Freenas