The paravirtual SCSI controller and the blue screen of death

For driver reasons, the default disk controller in VMware guests is an emulated LSI card. However, once you install VMware Tools in Windows (and immediately after installing the OS in most modern Linux distributions), it’s possible to slightly lower the overhead for disk operations by switching to the paravirtual SCSI controller (“pvscsi”).

I’m all for lower overhead, so my server templates are already converted to use the more efficient controller, but I still have quite a lot of older Windows servers that still run the LSI controller, so I’ve made it a habit to switch controllers when I have them down for manual maintenance. There is a perfectly good way of switching Windows system drives to a pvscsi controller in VMware, and it’s well documented, so up until a couple of days ago, I’ve never encountered any issues.

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