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Citrix XenConvert

During the course of our recent migration of some servers from physical to virtual, we had the need to migrate our existing Microsoft Exchange server. As I’ve mentioned before, this was an ancient Pentium D era box that was really struggling. In order to migrate, Citrix offers a free tool called XenConvert that can migrate most Windows based computers to a virtual machine on the fly.

Before moving the Exchange server, we had to have a trial run. I installed XenConvert on one of the staff room computers, a nice Core i3 computer with 4GB of ram. XenConvert installs easily enough, and the process to migrate the host isn’t difficult. It’s really a case of a couple of clicks combined with some thought on how you want the hard drive sized. With all of those choices done, I clicked continue and waited for the process to finish. The host was only running a 100mb/s network, but the overall hard drive size was quite small.

That being said, the process took hours. XenConvert needs a working area to store its temporary file, which in our case was a mapped drive off our main server.  After the process is done, XenConvert then feeds that file back through the host and into your XenServer. Again, this process takes hours, with the network card being pretty much maxed out. Despite all the waiting, the host converted successfully, which gave us confidence to tackle the Exchange server. That’s when the nightmare began.

On the last day of the first term, we shut down the Exchange services mid afternoon so that no one could access their mail and interrupt the process. All the relevant boxes were ticked, temporary drive mapped and so forth. It was then just a case of waiting. Unfortunately, the process was so excruciatingly slow that it made the Core i3 conversion seem like a speed demon. Granted, we were on a much slower box with more space used, but we did have gigabit ethernet to make up for that. No such luck. The process ran from about 14:30 through till 23:30 before it started the import procedure. Of course, by this time my colleague and I were long home, so monitoring the procedure was not simple. A few hours later, the server crashed due to the extremely high load XenConvert was placing on it during the import process. While nothing was damaged, the downside to this was that the Exchange services had restarted, allowing new mail in.

With heavy hearts, we had to start the procedure again. We had promised that no mail would be lost, so our hands were tied. I restarted the procedure again over that weekend, but this time I chose not to import the host into Xen automatically after conversion. We would rather do that ourselves while we were on site. This second attempt failed at some point to successfully convert for some reason.

For our third attempt, we decided to create an OVF package rather than have any import take place, as we could import the OVF package into Xen. Once again, the procedure took hours, but this time it finally succeeded. With the massive package sitting on our main server, my colleague started importing the OVF package into Xen. It was a harrowing wait, as the procedure carried a warning that it was experimental code! About 4 hours after he started, I remoted into work and breathed a sigh of relief that the procedure was done. My colleague had shut down the physical Exchange server already, so with a deep breath I started up the VM.

Much to my relief, it worked. From there it was just a matter of letting the VM pick up new drivers, install the Xen tools for proper storage and network card drivers and reactivate Windows. After all that and numerous reboots, I left the server to settle over night. It ran beautifully, and has continued to do so for almost 3 weeks now.

The overall impression I took away from this experience is that doing a physical to virtual migration on any host is a delicate time consuming procedure. The more information you have on the host, the longer it’s going to take. It’s also going to be problematic on older hardware that cannot handle the sustained high load when doing a straight import into Xen. Definitely a learning experience, but not something I want to do too soon again.

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