One of the greater mysteries around Hyper-V is probobly the difference between Fixed Size Disks, and Pass thru disks.
When Hyper-V was only RTM, one of the main buzz words was Pass Thru disks, and how they can improve your I/O’s inside the VM.
Basicaly, people are asking – can I set a fixed size disk that will consume the entire space of the disk, instead of setting it as a Pass Thru disk?
Now (actualy a couple of months back) Ben Armstrong, who is (If you still not formiliar with him) is the Program Manager for Virtualization Team in Microsoft, Published and article regarding that mystery.
The article talks about the different Cons and Pros of each disk kind, and here is a short description:
1. You cant use VSS to backup a machine with Passthru Disk
2. Its easier to move around a VHD file if you need to move your machine for archiving or personel backup solution.
On his article, Ben talks about 3 more deffrences – Data Safty, HW Monitoring and the most important (as I see it) issue – Performance.
Needless to say that there is an obiuos difference in performance between Fixed Size and Dynamicly Expending Disks, But according to Ben there is not much difference between Fixed and Passthru disks.
You can read more about the comparison by Ben Armstrong here.
I also suggest reading all the reset of his posts, as they are very interesting 🙂