I am thinking of upgrading my storage.
I currently have 1 120GB SSD as my OS drive but I constantly run out of space on it. Can I do a Raid 0 + 1 with 2 SSDs in RAID 0 with 1 HDD in RAID 1? Like 2 SSDs doing RAID 0 for speed but the HDD is the Parity drive in case one of the SSDs fails?
I don't think you can do that... Raid 01 is mirrored stripes, so you would need two raid 0 arrays, and I don't believe you can set up raid 0 on a single drive... Even if it was possible, I wouldn't advise it. You'd lose all the speed advantages of the SSDs because the in raid 1, the write isn't considered complete until it's written to both drives (or in the case of raid 01, both striped sets).
Just get a larger SSD to handle OS, programs and scratch. If something goes wrong with it, just replace it and reinstall. I never got the point of running redundancy on an os drive, at least not for home use. At worst you'll lose a couple hours reinstalling programs and whatnot. There shouldn't be anything on an os drive that isn't easily replaceable, unless you want to keep your game saves or profile settings on there or something. In which case, just back them up to your data drive(s).