Hello folks,
maybe this one is useful for you..
First of all, Windows 8 to go running from a VHD(x) can not be upgraded and you have to add a VHD file to a Hyper-V VM if you want to upgrade it.
1) Make sure you have the correct language pack installed in advance (if you download a upgrade Pack from the MSDN). Windows 8.1 will switch to the installation pack language automaticly, if you want to upgrade Server 2012 to R2 you are required to set and install the language pack in advance by your own.
2) Do not assign dynamic memory to the VM, it seams to be that the Windows 8.1 upgrade has a problem with dynamic memory and/or not enough memory is available during the boot time upgrade. This will create a “We couldn’t update…” Error after reboot.
3) If you’re using a KMS activated Windows 8 VM’s (which is common for company’s), make sure that the KMS Server is prepared for Windows 8.1 in advance and to update the KMS Productkeys for/in the VM’s (see also http://technet.microsoft.com/en-us/library/jj612867.aspx).
4) If you are using Windows App’s, before you can install or upgrade Windows App’s from the store you are “required” to set a temp folder for the Internet Explorer, sounds crazy but it’s really the case. (For Server 2012 -> R2 i got a similar error with code 0x8024600e, same like on Windows 8.1 but in this case it was not the temp folder; i need to resync the licenses in the Windows Store Option settings… Quite funny again.)
5) After the upgrade don’t forget to run the disk cleanup tool to remove ~6GB unused previous Windows 8 files (remove previous os) and upgrade log files, if you want you can also run a full clean up to keep the master VHD as clean as possible.
Update:
6) I forgot: The old language Packs and the Remote Server Administration Tools (RSAT) for Windows 8 are not compatible to Windows 8.1 (this includes Server 2012 R2 language Packs) and you have to reinstall it!
Cheers
Michael