How to make the Hyper-V VMs properly save and restart when rebooting the host

Serial Port: Yes, but you have to set up the COM as a Named Pipe on the host machine, so I don't know how this will affect your software.

Tape drives have been discussed here and the answer is an emphatical "no". You best bet is to install the tape drive into normal server (if your host machine is the bare-metal Hyper-V this won't work, it has to be the normal Windows install, and then have the Hyper-V role added) and expose it via iSCSI. There's plenty of software around that can do this. Starwind is one of them.

As for the fax card, I haven't seen any sort of PCI pass-through in Hyper-V. VMWare ESXi is way ahead of Microsoft Hyper-V on this front, however to use PCI Passthrough in VMWare you need to have fully supported hardware which may pose an issue if you've already purchased the servers, and there's no way to know for sure that your software will work the way you expect without trying it.

Colin,

This is most certainly a permissions issue. Even though the machines are saved they cannot contact the DC when they come back online. As a rule of thumb you can virtualize DCs but you should really follow MSFT's best practices as it is advisable to run a separate physical DC for failover reasons. For instance, using clustering and other services on the host machine that rely on a DC will all fail because the guest DC vm has not started.

Unfortunately if you are trying to handle recoveries from a failure there is no way to ensure proper automatic startup, where the machines boot in a specific order. I found a couple of solutions:

1. Hyper-V Startup Delay to the rescue: http://mctexpert.blogspot.com/2011/02/how-to-configure-start-up-delays-for.html
2. Boot them up manually. You can change the start-up type from auto or last state to off and then boot them once your host is up.
3. You can also change the mode from saved to shutdown and then add a boot wait timer by configuring a startup boot option select/delay to delay your IIS and SQL boxes from booting by like 2-5 minutes to give the DC a head start.
4. If you do ever get into clustering you can configure the HA settings to better control which machines boot when.