Drobo - RAID-like Redundant Storage Robot

How should we put Drobo redundant storage solution "robot"? From the looks of it, it is sorta like a JBOD with a certain RAID5 characteristics. Drobo can combine up to 4 SATA I/II HDDs of any sizes together to form a single virtual disk, which sounds like JBOD. However, say, if you install 3 250GB HDDs, you'll be left with only about 500GB of total usable protected space instead of 750GB. Drobo supposedly (don't quote on me) uses block-stripping with distributed parity to provide the best level of protection and tolerance. When one of the disks fail, there's no loss of any data. Software (Vista & Mac) will constantly bug you of this and the activity light adjacent to the screwed drive will turn red. Data repair begins as soon as Drobo detects storage replacement. More after the jump.

The company insists the Drobo's underlying technology isn't RAID, yet they are very secretive to what method it uses to protect your data. The user manual (PDF) focuses primarily on the ease of use, which is perhaps the most important to consumers. Everything from data mirroring to repair are done automatically in the background and drives are hot-swappable without interruptions to data transfer. You also don't need to reformat every time you upgrade as Drobo tricks Windows into thinking the size of the partition is 2TB. Beyond 2TB, the box will create a second pool of storage. If Drobo works as claimed, this should be an extremely robust, redundant storage, at least for those who are willing to drop $699. Oh, it connects to USB 2.0, no WiFi nor Gigabit Ethernet yet.