2) The windows setup didn't complain that it couldn't install on the 
LV, but once I clicked 'next', the Dom0 crashed and the server 
rebooted. A lot of output was displayed on screen but quickly vanished 
as the system rebooted. I'm trying to see if the output was saved 
anywhere. Any ideas why this could of happened and/or where the output 
might be saved?

I'd also like to add that after the server came back up, the md raid 
array started rebuilding. I wondering if that's just a coincidence (due 
to the forced reboot), or a sign of something wrong with the md 
integration with bcache?

I'm going to see if Windows installs natively on the md array (it's RAID 
10 btw) and post back here.