An interesting situation arose today with a Client who had a Windows 8 tablet and he wanted to make a system image backup to a 64GB USB Mass Storage Device and it wouldn't work - the error message was "drive not valid".
Before I go on, here is a link that helps guide you through the making a system image process on Windows 8.1.
So our discoveries,
Windows 8/8.1 has a slight anomaly when connecting USB devices - it will only backup to certain ones, depending on their type.
We connected a Windows 8 tablet to a USB OTG cable and connected a USB Mass Storage Device (Cruzer). The tablet wouldn't see the USB device as a valid drive/storage device.
We tried other USB OTG (On The Go) cables, an external Hard Drive and a USB Flash drive and they all worked - it was just the USB Mass Storage Device that didn't.
At this stage we tried a Windows 7 machine. Now, Windows 7 recognises the difference between a Hard Drive and a Device with removable storage - Windows 8 does not do this and it will not backup to a USB device that it detects as a Device with removable storage instead of a Hard Drive.
I'm assuming this is a "feature" to only allow backups to be done to "legitimate" Hard Drives. This is a bit confusing why they have done this, but they have done it so we need to accept and move on
So, if you have a Windows 8 PC, Laptop or Tablet and wish to take a backup system image in case of catastrophic failure, make sure you use a USB Hard Drive and not a "Mass Storage Device".
Don't forget to follow the link above for a "how to" on backing up Windows 8 system images.
If you want to get really technical, I have put a few links below that will help you understand the 3 different technologies