Disk geometry / parition offset.
Forgot to mention - for SSDs, don't forget to set your partition offset to allow for the 4K NAND block sizes and RAID striping .. boot from winPE or similar (before installing the OS), run diskpart:
select disk # (corresponds to RAID volume)
create partition primary align=2048
select partition 1
When installing the OS, use 'quick format' on the partition you created.
This can make *huge* performance differences for write speeds, as it helps reduce the build up of 'garbage blocks' over time, which plagues SSD performance. Some people were saying up to 300%.. I'm yet to quantify that with my own tests.