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Remember to use the Synthetic SCSI Controller in your Hyper-V VMs

A few minutes ago I was going over the Server 2008 Performance Tuning Guidelines1 and one of the recommendations for the Hyper-V role caught my eye, it was something I’d previously read before, but for whatever reason wasn’t currently implementing in my infrastructure: The Synthetic SCSI Controller.

The synthetic SCSI storage controller performs better over the emulated IDE controller, and while Hyper-V requires an IDE controller be present in a virtual machine for booting the VM, Microsoft recommends that an administrator mount any other VHDs with a high expected I/O rate to the synthetic SCSI controller mainly because of reduced CPU overhead, causing better performance. This is because the SCSI controller has a direct link to the VMBus, which gives it a performance advantage over the emulated IDE controller.

Another related recommendation is to mount a server’s paging file, and any log and database files to their own separate synthetic controller, and preferably keep these VHD files on their own set of physical disks, in order to minimize the risk of your disks becoming a bottleneck that can affect overall performance.


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