Active Directory and USN Rollback

Blog, how I’ve neglected you. Not for lack of things to write about, but crazy things have been happening lately. I’ve been designing and implementing Active Directory and everything that goes along with it (GPOs, file storage, backups, redundancy...and the list goes on).

I have learned quite a bit from this so far and would love to share with you what I have learned. Lack of time restricts what I can share right now, so perhaps I’ll share a little tidbit of information I learned very quickly: Never, EVER, under any circumstances, restore a virtual domain controller from a snapshot. This most likely will result in a USN rollback event, in which all domain controllers in the domain think that they’re the most recent version of the AD database, causing replication to completely fail. It is extremely difficult (if not impossible) to recover from a USN rollback. Trust me, I tried. My solution? Completely delete and redeploy Windows 2008 servers and setup AD completely fresh. And never restore from a snapshot again.

Check out a very complete explanation of what USN rollback is and how it all works here, and Microsoft's KB on USN rollbacks here.

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