Hyper-V and slow guest OS installation

I have seen a number of reviews and comments about the fact that while Hyper-V virtual machines appear to be quite fast once they are up and running – operating system installation seems to take quite a while.  The reason for this is relatively easy to explain.

With Virtual Server and Virtual PC we only had emulated devices to use – and as a result we spent a lot of time optimizing and tweaking the performance of these emulated devices.  When we implemented the emulated devices under Hyper-V we had to remove many of these optimizations due to the entirely different architecture of Hyper-V.  We did not, however, spend much time re-optimizing the emulated devices on Hyper-V because we had the new synthetic device architecture where we have focused our attention for performance tuning. 

This means that Hyper-V emulated devices are slower than Virtual Server / Virtual PC emulated devices – but Hyper-V synthetic devices are much faster than Virtual Server / Virtual PC emulated devices.

The catch here is that when you install an operating system you are almost always using our emulated devices – and you do not start using synthetic devices until after you have installed the operating system.

So in conclusion:

  1. Yes – operating system installation on Hyper-V is slower than on Virtual Server / Virtual PC.
  2. No – I do not expect this to change much for the first release of Hyper-V.
  3. Yes – once you are up and running and have integration services installed performance of Hyper-V virtual machines is much better than Virtual Server / Virtual PC.