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Virtualization Frontier : May 22, 2008

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Massive IOPS on ESX

Posted by ToddMuirhead May 22, 2008

They performance guys over at VMware have announced some really impressive IOPS testing results. Using three CX3-80 storage arrays they were able to push over 100,000 IO Operations per second from a single 4-socket server running ESX 3.5. Additionally, they reported the latency numbers which look very good as well.

I find this very interesting because it is in line with results that Kong and I got in our Exchange 2007 on ESX testing we did last year. We found that you could size storage for Exchange VMs the same as you size storage for Exchange on physical servers (up to the 2000 users in a single VM that we tested). Exchange is I/O intensive and is sensitive to any increased latencies. So while we didn't test a workload of 100,000 IOPS, we did see good storage performance with an application that is very sensitive to these kinds of things.

The other thing that I like about this test is that it is cool. As evidence I point to the cool graphs they included and the 495 15K RPM disks that were used.

Todd

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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

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