For speed and reliability and ease of backup I recommend:
Mirror the OS drive (C:) – this drive should be fast and I would recommend 10k drives – nice.
Raid 5 the data volume for storage (D:) for space and cost. Better yet, use external raid like a NAS device that can be shared without pc being on.
Mirroring the boot drive and only installing apps does two things. One, drive is mirrored for failover. Two, smaller size makes for quicker image backups (saved to the Data drive). With a program like Acronis True Image you can set a schedule to backup you drive periodically. Make a clean backup of base install for “factory” restore capability and then make weekly/monthly backups for quick restore of updates since original backup. This image backup insures that if your mirror raid fails and wipes out both drives, you can restore to new drive outside of array. I have had to break a mirrored array and my Dell pc which destroyed the data on the mirrored drives (who thought of this concept?) Also, the image allows you to upsize your drive(s). You can replace the mirrored drives with larger ones.
Many MoBo’s do not Raid 5 the boot OS and you may likely have trouble when using utilities and some software on the partitions. For various reasons, I do not recommend Raid 5 the boot drive. Also I have learned to keep data off the boot drive to keep it lean and easily replaceable. I now store _ALL_ data on file server or NAS drives to allow me to access data from any pc at any time, thereby making me not just drive fault tolerant, but pc fault tolerant! Downside is having to install software on multiple pc’s in case one crashes and licensing issue (i.e.: cost). But that aside, I took my older home office pc offline with 0 (ZERO) downtime and NO interruption of service! Although now I only have one pc L running at home.
How do I not use my C: drive for data? I store NO data on any personal pc (well, temporarily maybe, depending on the app, i.e.: video editing for speed of access and rendering). All standard apps (like MS office, email, scans, docs, etc. are all saved immediately to the network volume (i.e.: file server or NAS; either is a good option). (Note: file server can be just a shared low end pc that supports the Raid 5 volume, which is why any fault tolerant NAS can do the trick). The hard part of this scenario is making my apps default to NAS folder instead of My Documents. This can be done for some apps, but not all, so I simply placed a shortcut icon in My Documents folder to bounce to the NAS folder for saving data. I even trained my wife how to do this so her pc is also fault tolerant.
Products to consider: (2 examples that look interesting)
ReadyNAS NV+ at http://www.readynas.com/
Drobo at http://www.drobo.com/products_droboshare.aspx