Although not considered as a qfs tuning tip per se, I would strongly advice to align the starting block of a disk slice to a RAID boundary: when using EFI labels, the first slice starts at block 34 (i.e. an offset of 17kB). When the disk lun starts at this block, it will be badly alligned against the DAU, the segment size and stripe width. Make sure to start the disk slice on a well-aligned boundary (ex. 8192 blocks (4MB) which is at a RAID set boundary for all reasonable combinations of segment size and number of data disks).Failing to do so will trigger unnecessary cycles of the RAID’s read-modify-write.

Here's an excellent URL about the above : Partition Alignment Guidelines