I recently purchased a couple of USB 3.0 External HDD Enclosures to use for storage and backup; the idea was to have one act as backup to the other, with 4 x 3TB drives in total. However, the second drive in each is not accessible in either Linux nor Windows, and I could not determine the reason. 1. Situation The two enclosures are slightly different (couldn't find them in stock at the same time) yet from many little details appear to be the same Chinese base design with a tweaked outer shell. The models are: Sharkoon 2-Bay RAID Box Fantec MR-35DU3 The drives are Seagate 3TB Barracuda ST33000651AS, firmware CC44, all identical. From reading manuals and online sources, I determined that JBOD would be the optimal setup for my needs -- addressing the two drives separately in each enclosure would be important, making it easy to swap drives and mix&match them if needed; all the other modes implied the controller doing a combination of the drives. The software used was Debian GNU/Linux - testing/wheezy - kernel 2.6.39-2 and Windows 7 Ultimate. 2. Description of the problem Now, here comes the problem: every time I connect either of the enclosures to a PC using the supplied cable (tried a different one as well), only the HDD in the top bay is readable, the one below is detected yet errors out in various ways. According to the manuals, it should not happen: in JBOD, the system should be able to "see" two separate drives upon connection. This happens with both enclosures and any combination of HDDs (i.e. if I swap them, the same thing happens), so the HDDs are good and I think so are the enclosures (two different companies making similar products that failed in an identical fashion would be very unlikely). The top HDD can be used fine every time, I actually tried a speed test from Linux and got about 150MiB/s reads, so all is working as it should; the one below refuses to work every time. So the failure is consistent. To make sure this was not some obscure Linux bug, I tried the same under Windows 7, and the system also only created one drive letter for a drive of 3TB size (so it was only seeing one instead of both). Placing an older, known good, 2TB drive in the top bay made that the one recognised, so we have the same issue under Windows as well. Log entries under Linux (tested here with a 3TB and a 2TB drive so I could differentiate them; either one works in the top enclosure, in the test setup the 3TB one is on top). You can see them being detected, the top one is ok, but for the bottom one only errors: Jul 19 23:28:15 media kernel: [260150.582436] usb 6-1: New USB device found, idVendor=1ca1, idProduct=18ae Jul 19 23:28:15 media kernel: [260150.582440] usb 6-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3 Jul 19 23:28:15 media kernel: [260150.582442] usb 6-1: Product: Usb Sata Bridge Jul 19 23:28:15 media kernel: [260150.582444] usb 6-1: Manufacturer: SYMWAVE Jul 19 23:28:15 media kernel: [260150.582446] usb 6-1: SerialNumber: 39584B304C4E3441 Jul 19 23:28:15 media kernel: [260150.870412] scsi11 : usb-storage 6-1:1.0 Jul 19 23:28:16 media kernel: [260151.882087] scsi 11:0:0:0: Direct-Access SYMWAVE ST33000651AS CC44 PQ: 0 ANSI: 4 Jul 19 23:28:16 media kernel: [260151.882242] scsi 11:0:0:1: Direct-Access SYMWAVE ST32000641AS CC12 PQ: 0 ANSI: 4 Jul 19 23:28:16 media kernel: [260151.882677] sd 11:0:0:0: Attached scsi generic sg2 type 0 Jul 19 23:28:16 media kernel: [260151.882774] sd 11:0:0:0: [sdb] Very big device. Trying to use READ CAPACITY(16). Jul 19 23:28:16 media kernel: [260151.882857] sd 11:0:0:1: Attached scsi generic sg3 type 0 Jul 19 23:28:16 media kernel: [260151.882893] sd 11:0:0:0: [sdb] 5860533168 512-byte logical blocks: (3.00 TB/2.72 TiB) Jul 19 23:28:16 media kernel: [260151.883085] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.883582] sd 11:0:0:0: [sdb] Write Protect is off Jul 19 23:28:16 media kernel: [260151.883961] sd 11:0:0:1: [sdc] 3907029168 512-byte logical blocks: (2.00 TB/1.81 TiB) Jul 19 23:28:16 media kernel: [260151.884145] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.884570] sd 11:0:0:1: [sdc] Write Protect is off Jul 19 23:28:16 media kernel: [260151.884855] sd 11:0:0:0: [sdb] Very big device. Trying to use READ CAPACITY(16). Jul 19 23:28:16 media kernel: [260151.885286] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.885807] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.909595] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.910159] sd 11:0:0:1: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jul 19 23:28:16 media kernel: [260151.910163] sd 11:0:0:1: [sdc] Sense Key : Illegal Request [current] Jul 19 23:28:16 media kernel: [260151.910167] Info fld=0x0 Jul 19 23:28:16 media kernel: [260151.910169] sd 11:0:0:1: [sdc] Add. Sense: Invalid field in cdb Jul 19 23:28:16 media kernel: [260151.910172] sd 11:0:0:1: [sdc] CDB: Read(10): 28 20 00 00 00 00 00 00 08 00 Jul 19 23:28:16 media kernel: [260151.910182] quiet_error: 2 callbacks suppressed Jul 19 23:28:16 media kernel: [260151.910570] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.911153] sd 11:0:0:1: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jul 19 23:28:16 media kernel: [260151.911156] sd 11:0:0:1: [sdc] Sense Key : Illegal Request [current] Jul 19 23:28:16 media kernel: [260151.911159] Info fld=0x0 Jul 19 23:28:16 media kernel: [260151.911161] sd 11:0:0:1: [sdc] Add. Sense: Invalid field in cdb Jul 19 23:28:16 media kernel: [260151.911164] sd 11:0:0:1: [sdc] CDB: Read(10): 28 20 00 00 00 00 00 00 08 00 Jul 19 23:28:16 media kernel: [260151.911385] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.911902] sd 11:0:0:1: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jul 19 23:28:16 media kernel: [260151.911905] sd 11:0:0:1: [sdc] Sense Key : Illegal Request [current] Jul 19 23:28:16 media kernel: [260151.911908] Info fld=0x0 Jul 19 23:28:16 media kernel: [260151.911910] sd 11:0:0:1: [sdc] Add. Sense: Invalid field in cdb Jul 19 23:28:16 media kernel: [260151.911913] sd 11:0:0:1: [sdc] CDB: Read(10): 28 20 00 00 00 00 00 00 08 00 Jul 19 23:28:16 media kernel: [260151.912128] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.912650] sd 11:0:0:1: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jul 19 23:28:16 media kernel: [260151.912653] sd 11:0:0:1: [sdc] Sense Key : Illegal Request [current] Jul 19 23:28:16 media kernel: [260151.912656] Info fld=0x0 Jul 19 23:28:16 media kernel: [260151.912657] sd 11:0:0:1: [sdc] Add. Sense: Invalid field in cdb Jul 19 23:28:16 media kernel: [260151.912660] sd 11:0:0:1: [sdc] CDB: Read(10): 28 20 00 00 00 00 00 00 08 00 Jul 19 23:28:16 media kernel: [260151.912876] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.913439] sd 11:0:0:1: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jul 19 23:28:16 media kernel: [260151.913442] sd 11:0:0:1: [sdc] Sense Key : Illegal Request [current] Jul 19 23:28:16 media kernel: [260151.913445] Info fld=0x0 Jul 19 23:28:16 media kernel: [260151.913446] sd 11:0:0:1: [sdc] Add. Sense: Invalid field in cdb Jul 19 23:28:16 media kernel: [260151.913449] sd 11:0:0:1: [sdc] CDB: Read(10): 28 20 00 00 00 00 00 00 08 00 Jul 19 23:28:16 media kernel: [260151.945227] xhci_hcd 0000:03:00.0: WARN: Stalled endpoint Jul 19 23:28:16 media kernel: [260151.945863] sd 11:0:0:1: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Jul 19 23:28:16 media kernel: [260151.945866] sd 11:0:0:1: [sdc] Sense Key : Illegal Request [current] Jul 19 23:28:16 media kernel: [260151.945870] Info fld=0x0 Jul 19 23:28:16 media kernel: [260151.945871] sd 11:0:0:1: [sdc] Add. Sense: Invalid field in cdb Jul 19 23:28:16 media kernel: [260151.945875] sd 11:0:0:1: [sdc] CDB: Read(10): 28 20 00 00 00 00 00 00 08 00 (...) and so on for like 10 seconds until it gives up (...) 3. Question So, my question would be: what is causing this? Am I missing something, should I configure things differently, is this a known limitation? Searching online for more information did not yield any useful results... Thank you in advance for any help!