Hi,
While what shivakv says is true there are some herrings.
First is what kind of file system are you using on the external USB?
You'll need to use a file system that can be shared between both operating systems. FAT32 sounds OK, but realize that nowadays the split disk option can make slices to grow beyond 4GB per slice (which would give you disk corruption when on FAT32)
The maximum size a slice can get depends on the total size of your virtual disk. VMware changed the logic on this in Fusion 7 / Workstation 11. Sorry can't find the specifics on that at this moment. Ok, found it, more details on this -IMO silly change- here: https://communities.vmware.com/thread/498924#2463241
Also note that while the motherboard is virtualized, the CPU is not, so if your CPU is significantly different then you still might have to re-activate windows when switching between Fusion and Workstation.
three... make regular backups!
and lastly if you use things like shared folders realize that your folder structure on the windows host is different from the Fusion host. OS X does not have a concept with C:\ drives etc.. (nor the backslash notation)
--
Wil
