Windows Server 2012 R2 cache drive size for parity drives
It turns out the maximum a parity drive write cache size can be is 100GB. I have a 500GB SSD (~480GB real capacity) so the maximum write cache size I can make for a volume is 100GB. I suspect I maybe able to create multiple volumes and have each of them with a write cache of 100GB. Until then this is the biggest it seems you can make for a single volume, so MS solves that issue of having a too large write cache.