I currently have this setup:
Server: (Debian Jessie)
sda = 1 TB drive with debian/urbackp 2.0.33
sdb = 4 TB ext4 drive for storage only
Client: (SBS2003)
C: = Windows, 60 / 415 gb | Shadow Volume Copy enabled, 4096 Mb
F: = Data, 450 / 500 gb | Shadow Volume Copy disabled
My first full backup acted a little oddly. It took 15 hours for the C drive, and was stuck going very slowly 70 KBit/s for ~12-14 hours, then skyrocketed to 260 MBit/s for the last 1-2 hours. Very odd. F drive copied as expected, taking ~6 hours for the 420 GB, averaging 160 MBit/s.
The incremental backup of C drive also worked fine last night, taking ~32 minutes for ~8 GB of data @ 36 MBit/s.
There was no incremental backup of F drive last night. Nor any messages in the log saying it was trying to backup F. I am guessing it may be the Volume Shadow Copy not being enabled at the moment, but I wanted to verify if that could be the problem. (Or if I just messed up a setting somewhere else.)
Update:
Well I am not entirely certain why, but the system did do an incremental backup of F drive on 9/2, but not C drive. Then did incremental backups of both C and F drive on 9/3 to 9/5. So it does appear to be doing them both now.