Converting Physical Database Servers to Virtual Machines

I’m in the middle of tough project right now, a large client is trying to convert a large number of physical SQL Servers to virtual machines. They’ve done most of the right things—the underlying infrastructure is really strong, the storage is more than an adequate, and they aren’t overprovisioning the virtual environment.

Where the challenge is coming in is how to convert from physical to virtual. The classical approach, is to build new database VMs, restore backups from the physical to the VM, and ship log files until cutover time. However, in this case there are some application level challenges preventing that approach (mainly heavily customized application tier software). Even so, my preferred method here is to virtualize the system drives, and then restoring the databases using database restore operations.

This ensures the consistency of the databases, and rules out any corruption. Traditional P2V products have challenges around handling the rate of change in databases—many people think read only database workloads don’t generate many writes, but remember you are still writing to a cache, and frequently using temp space. What challenges have you seen in converting from virtual to physical?