As long as it isn't a floppy disk it will work.
I'm not aware of hard drives recommandation because it doesn't really play a big role in OBIEE (OBIEE doesn't store/contains data). Only things written on your disk would be cache if enabled and temp files if you are asking your BI to do the job of a database.
One thing that is there is the repository file. It may be slow to access from a clien in online mode.
Then the disk could be a reason I think.
Accessing the RPD in online mode in 12c (you don't post any version, so let's assume most recent) is going to be slow because of your network and various other factors but not really the disk. The RPD isn't supposed to be 10Gb, and it's also not stored as RPD itself.
And working online is anways going to be slower than offline just by design.