But, on to the TR4U:
Positives: Negatives:
Good-looking and quiet. Drives seat well and stay in without mounting screws. JBOD or spanned mode works well. Drives stay cooler than other solutions I've tried (case is well ventilated on front and sides, and the big fan pulls the air out the back). Front LED changes color when a drive is being used. Front power button is handy, and must be held for 3 seconds to turn unit off. No power brick -- transformer is built into the case. Thumbscrews make it easy to remove cover if you need to do so; I just insert the drives and run then without mounting screws, so I don't remove the cover, I just get to everything via the front door. No software required for JBOD or spanning, it all just works. I haven't had to use tech support since I bought it, but they answered pre-sales questions admirably quickly. The unit itself is just a simple box, but is glossy black, and the vent perforations in the front door and side panels are very small.
2 TB limit on spanned drives (limitation of the on-board controller, as it's mentioned in the manual), and you can only make 1 volume per drive set, so leftover drive real estate must go wasted. Drives go in and seat fine, but are difficult to remove, because the drives are close enough together that a hand can't get a good hold -- I've tried using pliers, which scratched up my drive fronts, and am now using a screwdriver that I bent to a 90-degree L on the end that fits nicely in an hole in the bottom front of my Seagate drives… removing the cover and using the provided drive mount thumbscrews would obviate this problem. Manual suffers from translation difficulties, but everything is easy to do. DIP switches that control spanning and power modes are inset and thus well-protected, but hard to get at unless you turn the unit around (as with all such switches; but I'd prefer to have these on the front). Fan has blue light that might be annoying in a darkened room.
I'm using this enclosure and Backup Exec's Backup-To-Disk option to back up several of my department's servers, and it works very well. I use three sets of 3 750 GB drives, and rotate drive sets once per week -- full backups on Friday, incremental backups Monday through Thursday; and I have the drives in JBOD mode, and configure the drive sets as members of the device pool, and allow two jobs to occur simultaneously (but only one job per drive), and the USB seems to handle that just fine -- I'm getting throughputs (as calculated by Backup Exec) of anywhere from 300-600 MB per minute per drive with two drives in use at the same time. Swapping spanned drive sets with the power off results in no problems, all data is retained (although I do label my drives and make sure I put them in the same position top to bottom, I'm not sure if this is important). I would buy this again, or might go with the 8-drive version that allows the use of drive trays for easier drive changes (although the trays, at $20 each, might be too expensive).