P2V of Domain Controllers – Online or Offline?
We know that SCVMM can convert physical machines into virtual machines with all work necessary to make this transitioned machine still boot and function correctly. This is a great feature that customers use daily. This work is done usually while the server is still running as an Online P2V. If you have ever stopped to think about how the P2V process works (or read the TechNet article explaining) then you know that the first part of the process is simply a volume shadow service (VSS) snapshot made of disks. This is the same technology used by Windows backup and most third party storage software.
The trick is to capture a state in time while the machine is running. For most systems this is a great solution. For some, this poses questions. SQL, Exchange and Domain Controllers write to databases at a high rate. By the time the snapshot is made quite a bit may have changed in the database. Also, as good as the technology is, this is pushing the limits of functionality. SQL and Exchange systems benefit from acquiescing the SQL or Exchange service prior to P2V (or any backup). This reduces disk writes and ensures database integrity.
Domain Controllers are another matter. If there is more than one in the domain there is replication between them. If the state of one is captured while it is processing Active Directory transactions, then brought online as a VM later, the VM and physical versions of this DC may be different. Additionally, there is the concern of USN journal wrapping during the snapshot process. Then again, online P2V of DC’s works well on a daily basis for many people. The alternative is to perform the conversion offline, an Offline P2V. What is the right choice?
Do you want the new VM created from the DC to function correctly and have no issues with the rest of your Active Directory domain? Yes? Good choice. Perform the P2V Offline. Now I refer you to an article written by Sander Berkouwer. This covers the entire process better than I have seen put together before. Nice pictures too. The article describes online and offline conversions, and the implications of Online P2V of Domain Controllers. Then it walks you through the process while addressing four very solid recommendations. Enjoy the article. Keep it as reference.
Thanks to Sander for allowing me to link to his work!
Active Directory in Hyper-V environments, Part 6
TechNet article referenced…
TechNet - P2V: Converting Physical Computers to Virtual Machines in VMM