I have spent some more time with Virtual Machine Manager (VMM), Microsoft's new Virtual Server2005 management tool. My somewhat positive impression which I expressed in two earlier posts about VMM has been dampened a little since then. This is mostly due to the fact that VMM seems to be a bit unreliable.
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In my first test, I realized that the VMM admin console was quite unstable. I assumed that those problems were related to the virtual environment where I tested VMM. For my second review, I just explored VMM's features on a physical installation. I didn't encounter any serious problems then. But the longer I work with VMM, the more troubles seem to arise. I am obviously not the only one struggling with VMM these days. Microsoft's Technet forum is full of unanswered questions and bug reports.
Of course it is possible that my problems were caused by my own errors or that they were somehow related to some special conditions in my test environment. However, I installed VMM on a freshly installed Windows Server 2003 R2 SP2 system. I tested it with two new installed Virtual Server hosts. The whole installation and configuration of VMM is fairly simple. There is not much room for mistakes. And if an application crashes on a newly installed server, usually a bug is the culprit.
So here are the problems I encountered in my tests so far:
VMM Admin Console
I already mentioned it before. Virtual Machine Manager's Admin Console is quite unstable. It completely crashed a couple of times. In some cases, I was able to reproduce the failure. When I tried to modify the hardware of a certain virtual machine the Admin Console would always shut down, improperly. This was independent from the location where I run the Admin Console. It crashed on the VMM server (Windows Server 2003 R2 SP2) and also on a Vista machine.
VMM service crashed
This happened only once. After one of the crashes of the VMM Admin Console I wasn't able to reconnect to the VMM Server because its service was shut down, too. I had to restart it. The event log only contained a cryptic "Net Runtime 2.0 Error". I didn't try to find the cause of the problem since VMM seemed to work fine again afterwards.
All in all, I cloned about 10 times. More than half of them failed in the first place. I cloned from host to host, and on the same host. Usually the cloning process would just be interrupted after a while. However, in all cases I was able to resume cloning using VMM's repair feature. The error message always indicated that the connection to the Virtual Server host was broken. That was never the case, though. I always checked the connection immediately after the cloning process failed. I also ran some tests to make sure that there is no network problem.
Changing hardware configuration
This problem might be related to the cloning issue described above because it only happened with cloned virtual machines. Sometimes I wasn't able to change the hardware configuration of a virtual machine. In those cases VMM always complained that the virtual machine has to be stopped first or that it is in safe mode. This was never the case, though. I wasn't even able to mount an ISO image in those VMs using VMM. However, it always worked fine when I configured these problematic VMs with Virtual Server's own admin interface. I concluded that it must be a VMM bug.
Access denied to virtual machine
After I updated one of these cloned VMs using the Virtual Server Admin Console, I was no more able to manage it with VMM. VMM would always complain with this message: Detailed Error (2910). (Access is denied (0x80070005)). So VMM didn't have "appropriate permissions" to access this VM, anymore. However, all other VMs on this host were still manageable. The problematic VM also seemed to work fine. I didn't encounter any problems when I managed this virtual machine using the Virtual Server admin interface. In the end I was able to configure it by using VMM's repair feature again. It seems that this the most important feature.
Merging of checkpoints on a Linux guest system
Checkpoints are what VMware calls snapshots. They allow you to restore a virtual machine to a prior state. It is possible to merge several checkpoints to free hard disk space. When we tried this feature on a Linux guest system (SuSE Linux 10.0 Enterprise) a folder with all its contents was gone after the machine rebooted. The strange thing is that no checkpoint was created before or after this folder was added to the guest system. Only this one folder was deleted, everything that was added after this folder was created was still there. I suspect that VMM had problems with the large size of this folder (about 100 GB). Since then, I only use this checkpoint feature very cautiously.
There also were a couple of minor issues. The function didn't work at first, but when I tried it again later, VMM recognized its mistake and allowed me to proceed. For example, I once wanted to shut down a virtual machine from the VMM Admin Console. VMM complained that this feature is only available if the Virtual Machine Additions are installed. After I reassured myself that they were running on the guest, VMM admitted its wrong assessment of the situation and let me shut down the VM.
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There were other similar cases. I won't list them all here. I think you got the picture by now. In my test VMM was quite unreliable. However in most cases I was able to get what I wanted in the end. I still like VMM because its user interface certainly is a major improvement to the old fashioned Web-based user interface of Virtual Server 2005. And of course VMM's most interesting feature is its ability to manage multiple Virtual Server hosts with just one user interface. So at the moment I am undecided if we will work with Virtual Machine Manager in a productive environment.