I have a 2012 rMBP with a 256GB drive, on which I've installed Windows 8 into a 45GB partition. I use a Thunderbolt display, to which I have connected a 1TB external Firewire 800 disk drive. I use that drive to store my iTunes library and such. Well, I would like to install some additional software under BootCamp, but my BootCamp partition is almost full, and I really don't have the space to expand it. So my idea was to create a partition on the external drive for Windows, and install the software on that. I shrank the Mac OS X Extended Journaled parition on the external drive from 1TB to 900GB. Then in Windows, I created a new NTFS volume. When I tried to format the volume, the drive would disappear from Windows. I had to disconnect and reconnect the drive to make it appear again. But every time I'd try to format it, it would disappear. When I booted back into OS X, I found that both partitions on the external drive had been wiped out. I tried to repair with Disk Utility, but it didn't work. I had to reformat the partitions and recover my data from my Time Capsule (thank god for that). This time I formatted the Windows partition with ExFAT from Disk Utility. When I booted into Windows, it now recognizes the partition, but I'm still getting some flaky behavior. I'm trying to install Steam to it, and it keeps crashing during its update process. TL;DR - I'm having issues with a Windows-accessible partition on a previously Mac-exclusive FW800 drive. Is there something I'm missing in setting this up?