On the TechTuesday chat yesterday the topic was Selecting a Server for Virtualization, and we had an excellent discussion. One of the points that came up was the importance of understanding VMotion compatibility between different servers. On easy rule is that it is not possible to VMotion between AMD and Intel processors. As these are completely different processors in many respects it is easy to understand how it is not possible to move a running VM from one to the other with no downtime. The next aspect that VMotion will not work across different generations of processors. The difficulty here is that processor generations do not always line up with Dell server generations. So even if you have all Dell 9G servers, there are cases where VMotion will not work.
It really comes down to the instruction set that each processors is using. A running VM has identified the processor that it is running on and is expecting a certain instruction set to be available. If this were to suddenly change in the middle the OS would not be able to cope or adapt and would most likely crash. There has been some work done to improve the situation - but as of today it is still an issue.
The answer to this problem is the compatibility matrix that our virtualization engineering team has put together and updates as new servers are released. It is important to consider this matrix when selecting a server if VMotion is in use.
Todd
