I've already allocated about 12GB for the C: drive system restore. I noticed while setting it up that there is also a D: drive.
This is my first time seeing a D: drive and it's on the Acer laptop I just got. From what I can tell it doesn't really have anything inside. Yes I've made sure to have it show me hidden folders and there was msdownld.tmp which I deleted since it's just an empty download temporary folder.
The D: drive is also taking up most of the space and downloading stuff still going into the C: drive.
From what I've been able to find on forums is that it's not important and I should just merge the D: drive back into the C: drive. I agree with this but I wanted a little advice before I do so. Don't want to accidentally break something.
Update: I've also looked at disk management and it seems the recovery drive is not in the D: drive before anyone asks that.