Came across an interesting issue. I was helping someone migrate from P2V using the same method I did however they want to P2V one of their 2 DCs - I left both of mine P for the time being. After looking at best practice it seems the most foolproof was to bring online a temporary physical server, promote to DC, demote the "to be virtualised" then backup/restore before promoting again when running virtualised (then demote the temporary one when happy). Windows backup/restore has worked for all our servers when I P2Vd and it left us the possibility of bringing the old one back if something goes wrong.
Looking at the best practice it seems that you should use a vSCSI disk for the AD directories to avoid caching anomalies on the IDE controller (there is a KB update that mitigates this for 2k8R2 and 2k12 but the best practice papers still say use IDE mounted disk not SCSI). However, how can you restore to a scsi host disk from windows restore? I couldnt get a driver to work that would allow the 2008 disk to see the SCSI disk does anyone know which driver to use? In this instance what would you do for a bare metal restore (from a regular windows server backup) in these cases? If you cant see a vSCSI disk in windows restore then that makes windows server backup is next to useless...
Host is 2k12, guest is 2k8.
Or are there people happily using a 2k8 (notR2) guest DC on 2k12 host? No caching issues?
Last edited by KK20; 25th October 2013 at 01:23 PM.
I'll answer my own question for anyone else who was wondering.
Loss of consistency with IDE-attached virtual hard disks when a Hyper-V host server experiences an unplanned restart
This patch addresses the caching issue. It seems that because you cannot disable caching in hyper-v then AD could fall to pieces as previously a guest would get a spurious answer after requesting caching disabled (but in actual fact it had not). As long as this patch is installed (I suspect the DC would need to be promoted AFTER this patch) then all will be well - the host will actively refuse to disable caching for the guest, the guest will warn in event log and continue to save without caching (rather than blindly assuming that caching has been disabled).
Last edited by KK20; 25th October 2013 at 04:24 PM.
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