I have set up Ubuntu and Windows 10 as dual boots on my computer. I read in many cases that one should disable Windows Fast Startup to prevent data loss due to Windows's hibernation files. But in my case the two OSs are installed on separate hard drives.
Would I still need to disable fast boot?
For proper dual boot of Ubuntu (or any Linux) and Windows 8/8.1/10, the now default Windows fastboot should be disabled. The os-prober usually fails to recognize Windows.
Considering that you won't be mounting the Windows system partition for use in Ubuntu (best practice) but you may have a separated NTFS data partition shared for both OSes (also a best practice), then Windows with the default behavior will hibernate the said partition as well, therefore it's recommended to disable fastboot in any dual boot scenario.
This comes down to how you boot between the two. A shutdown of Windows will save the "fastboot" information for the next boot but a reboot will not.
So if the last boot was running Windows and shutdown you should boot into Windows first and then reboot into Ubuntu. Otherwise if you were last running Ubuntu you could boot into either.
Also someone correct me if I'm wrong but I believe booting into Ubuntu while Windows is in fast boot hibernation only prevents you from mounting the NTFS partition under Ubuntu.
I have never disabled fast boot or experienced data loss when booting between Windows 8, Windows 10 and Ubuntu but I suppose it is a risk.
In regards to this being a comment rather than an answer I'll try to be more clear
My answer is you don't "need" to disable fastboot in Windows in order for dual boot to function. However bearing the limitations in mind listed above:
You may want to consider disabling fastboot for convenience and data safety.
