Somebody said that with a RAID 1 drive, 4TB will be 2TB of storage, but if the controller goes bad, then the whole drive will go bad — unless WD can send you a new enclosure? (stated in http://www.amazon.com/Western-Digital-Book-Studio-WDH2Q40000N/dp/B002BH3ZCU/ref=sr_1_1?ie=UTF8&s=electronics&qid=1277567998&sr=1-1 )
Cost $399
So is it just better to buy 2 drives — each one 2TB, and use SyncToy to sync them up by using mirroring? There will be two power adapters then…
Total cost: $260 plus more electricity probably
It also sounded good to buy RAID 5, which I heard, with 4 of 2TB drives, you get 6TB of capacity, not 4TB. But the WD RAID 5 drive on Amazon.com also has bad reviews
Cost: $294
Best Answer
Depends on what you want. If it is important for you that there is no downtime when one of your disks fails (and a disk fail has a much higher probability than an electronics/controller fail), use a RAID.
If it is more important that your data is safe (i. e. a backup), use separate disks and sync them manually (maybe even keep multiple generations as you can always accidentally delete important files).
A RAID is not a backup (in the rare case that the electronics fail). You will need a backup (at least if you think your data is somewhat important), but you will only need a RAID if uptime is important to you.