I have a 4 slot fantech jbod. I put 3 small hdds in it. I use it for my sacrificial old drives for downloads, p2p, etc.
Despite being usb 3 (dont ask me what rating / speed / yearly-changing nomenclature), it can't transfer files quickly, and trying to do transfer operations from more than one drive at a time will tank the transfer speed of all but one to next to nothing.
30-50MB/s in the best case if I'm reading from one drive to write on a disk that is not in the JBOD a large file. I've almost managed 80-100 from one jbod disk to another for a large file while doing nothing else. I'd be more than happy with 40MB/s.
However this is the best case scenario and it's almost never the case. having jdownloader and torrent operating (my internet speed is about 5MB/s) slows this down, and most importantly, trying to do one transfer from one disk and another transfer from another disk will result in the transfer speed to a more typical 5-12MB/s while the other will be at 100kbps. to move a completed torrent to another location takes much longer than it should even if I'm not doing other transfers (but while I'm downloading other stuff)
Is it an actual matter of transfer speed? Did they skimp on the controller and it can't handle the disks at once or the transfers? do the write operations weigh too much on the jbod or the disks to allow transfers too?