RAID via the Disk Utility
The LaCie 5big Thunderbolt is built around a number of ASMedia ASM106X controllers. It doesn't have a true RAID controller, however. To bundle disks you can use the Disk Utility in Mac OS, but standard it comes in RAID 0. You can create configurations like putting a couple disks in mirror, putting a couple disks in RAID 0, or as separate volumes. RAID 5 is not possible. Windows is not (yet) officially supported, and we were unable to get the LaCie 5big Thunderbolt to work in Microsoft's OS.
There is a big difference between the 5big Thunderbolt and the Promise Pegasus R4 and R6. These fit four or six disks, but have a true RAID controller as well.
The absence of RAID 5 makes it so that you have to consider how you will use the LaCie 5big Thunderbolt. If you work with large video or photo files, it can be useful to have this much storage just a cable away. Or as an accessory for your Apple MacBook Air, Pro or Pro Retina. However, we would not recommend using the 5big Thunderbolt as back-up device if you leave all the disks in RAID 0. But if you put two disks in mirror with the other three in RAID 0, then you have an interesting configuration.
It's a bit of a shame that the 5big Thunderbolt comes full of hard disks. It makes it an expensive matter getting acquainted with the LaCie 5big Thunderbolt, and you're also stuck with the hard disks that LaCie chose. Using a couple SSDs along with a couple hard disks would be a useful setup. If you want to attempt that, you will need to use a bracket because the trays are designed for 3.5-inch disks only.