Am I reading this correctly: stablebit will automatically duplicate folders on separate drives. If I wanted 100% file redundancy I would need a full 2x the number of storage drives?
If you choose to have a folder duplicated, it will ensure that every file in that folder exists on two separate hard drives. The files will be stored in an NTFS format so you could manually verify that the same file exists in two places (but it will feel like a single file from the user perspective). That means that you have to have at least two hard drives for that functionality.
It is true that you will be eating up twice the space for each file saved so similar in some ways to a RAID 1 configuration. On the upside, it can use different sized disks and you can bring them in and out of the storage pool with little hassle. If you've ever had a RAID 1 setup where one drive goes down and you try to incorporate a different sized drive into the array, it can be a hassle.
Given the relatively low prices of hard drives nowadays, I'm pretty comfortable with needing twice the storage space for each file.
You can configure on a folder level which data you want duplicated or not, and you can change your mind easily. For example, most of my movies were just a single copy but at some point, I decided that I had put enough effort into ripping them that I would be peeved if a disk failed. So, I turned on duplication for that particular folder and hours later, they were all taken care of.
Jotham