I have an XPS 8300 with 2x1.5TB drives set up w/o Raid as drives C: and D:.
I was wondering if I could mirror just the C drive and whether it would significantly slow my machine down doing the 2 writes. I don't really need to mirror the D drive as it is a data drive and is backed up to external drives.
Also, I was told that I could put in a hardware Raid that would speed the dual writes up - would this require the use of another of the machines slots?
Assuming your system files and data files aren't using too much of the 1.5 TB, then running RAID 1 would be the most convenient way to keep everything backed up. You could even partition your first drive into C system and D data partitions so everything appears exactly as it's set up now.
The Dell technology guide for your system has instructions in the "Working with Drives" section on how to set this up.