As far as I can tell, there isn't anywhere on Microsoft's sites or documentation which state DFS + Bitlocker is supported or works in Windows Server 2008. The DFSR FAQ mentions DFSR does not work with EFS, but does not mention Bitlocker. This is the case more than likely due to Bitlocker being so far below any user-mode application that the applications (such as DFSR) simply do not know that it exists. Consequentially, testing is not needed for every single scenario of Bitlocker + <app>. Microsoft does officially support the DFSR + Bitlocker combination on Server 2008.
Ned Pyle, a Microsoft enterprise support engineer, volunteered to do some performance testing of Bitlocker + DFSR. The net result was Bitlocker+DFSR worked great. However, there was a ~%25 degraded performance in replication time with Bitlocker turned on. This is to be somewhat expected due to the overhead of encryption, however, having a faster disk subsystem than what was tested with will more than likely significantly improve performance with Bitlocker enabled and reduce this gap. Again - please keep in mind this is a worst-case scenario considering the given hardware and configuration.
Here are the detailed results from the testing:
- Win2008 Enterprise
- Hardware - 2.4Ghz Quad Core, 4GB RAM, single 250GB non-SATA IDE drive
- Default DFSR config, no antivirus realtime scanning running
- Effectively worst case from disk perspective (very slow IDE disks shared with OS (%systemdrive% only))
- Replication time based on delta between event 4102 and 4104 on downstream.
- Between each pass the RG's are deleted as is the replicated folder data
1GBit NIC’s (Intel 82566DM-2 WHQL inbox driver 126.96.36.199)
- Switched 1GB network, probably under fairly high load as it’s the NC test lab and is usually moving a lot of multi-cast imaging data all the time.
- No hops, same Ipv4 subnet.
5.05 GB (5,432,323,831 bytes)
Data set made up of: 2008 platform sdk, office 2007, visual studio 2008, r2 sdk, vista sdk directories 51,614 files, 5,680 folders
baseline1 - 0h:50m:29s
baseline2 - 0h:49m:51s
baseline3 - 0h:50m:44s
avg - ~50m
bitlocker4 - 1h:05m:14s
bitlocker5 - 1h:07m:25s
bitlocker6 - 1h:06m:10s
avg - ~66m (~25% slower)