change the basic history storage from C drive to D drive
assuming you have 800xA 6.0, use the System Configuration Console:
Clients and Servers -> System Directory Configuration,
Then configure Basic History to use "ServerData2" and set the Path as you like for each Server.
I never tried that on running Systems, but i think in a redundant system you may need to change only one node at a time to not loose all the existing History Data.