I was attempting to migrate 2 virtual machines that are domain controllers between 2 datacentres running ESX 3.5 and ESX 4.1. I was advised to shut down both domain controller at the same time during the migration process. This is to avoid USN Rollback and other replication issues.
The following are the steps that I was planning to perform:
1. Shutdown both DC.
2. Copy both VMs files across to new datacentre using Veeam FastSCP (connection to both vCentre through IP address instead of hostname)
3. Power them up at new datacentre.
4. Configure Network interface/DNS/DHCP for both DCs in new datacentre
I have tried to use Veeam FastSCP rather than VMware Standalone Converter is because its copying rather than converting. Someone also suggested that I use backup and restore app like Veeam backup and replication software.
Sounds like a simple job, but after shutting down both DCs, the transfer rate using FastSCP is so slow registering only 1KB/s as oppose to the normal 1MB/s (or more).
When that attempt to transfer failed, I tried to cold clone both DCs resulted in the both ESX hosts get disconnected. I have tried troubleshooting by referring to this –
VMware KB – Diagnosing an ESX Server that is Disconnected or Not Responding in VirtualCenter
It seems that the DNS being down is the caused of all unusual occurrence. The moment I powered up the DCs via VMware console command, the ESX host were able to connect to the vCentre again.
How can I avoid such a pitfall again? Am I doing it correctly? Any help would be greatly appreciated! Thank you.
Best Answer
I don't see any reason to shut down both DC's at once. USN rollback is only going to be an issue if you restore a point in time copy\clone\snapshot of a specific DC after the source machine has been allowed to continue on. For your migration, shut down a DC and move it\copy it using whatever mechanism works best then restart it on the new site. At that point make 100% sure that the source VM can't be restarted as that will cause USN rollback. Once you have one DC moved successfully, repeat the process for the other(s).
Provided both sites are active and can see each other you can migrate the DC's individually while still keeping at least one active at all times, which you will need to do if the migrations take any length of time at all. As you have found out with the vCenter issues that arise when your DNS goes down you can't do much in an AD managed environment when you take all AD services down.
If both sites are completely independent of each other - so that when a DC is migrated to the new site it cannot communicate with the original site - then you will have to be much more careful and both DC's will have to be shut down for some period of time to ensure USN rollback doesn't happen. You can migrate the first DC you want to move while keeping the other one active but you must keep that DC powered off on the original site until you have migrated the second DC. If you don't then there is a risk of USN rollback.
To get around this I'd suggest the following. Make a clone of each DC on the source side using vCenter. Be very careful with these as you do not want to power them up with network connectivity on the source site.