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I have a 1.5TB WD external USB HDD and two Ubuntu systems, both 'precise'. When I plug the disk on system A it doesn't show up on the output of sudo fdisk -l nor is it automatically mounted (note that that wasn't always the case - it used to appear in the past). When I plug it on system B (again Ubuntu precise) it shows up when I do a sudo fdisk -l (output appended at the end).

What does this discrepancy between the two systems point to and what kind of diagnostics should I run / tools I should use to troubleshoot the problem?

UPDATE: When I plug the device on a USB port on System A I see the following when I have a tail -f /var/log/syslog running:

output of tail -f /var/log/syslog on System A

Sep 16 01:15:09 thorin kernel: [ 9883.556173] usb 2-2: new high-speed USB device number 7 using ehci_hcd
Sep 16 01:15:09 thorin mtp-probe: checking bus 2, device 7: "/sys/devices/pci0000:00/0000:00:13.2/usb2/2-2"
Sep 16 01:15:09 thorin mtp-probe: bus: 2, device: 7 was not an MTP device

output of sudo fdisk -l on System B

$ sudo fdisk -l

Disk /dev/sda: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00070db4

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048  2905114623  1452556288   83  Linux
/dev/sda2      2905116670  2930276351    12579841    5  Extended
/dev/sda5      2905116672  2930276351    12579840   82  Linux swap / Solaris

Disk /dev/sdb: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x9c849c84

  Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *          63   488375999   244187968+   7  HPFS/NTFS/exFAT

Disk /dev/sdg: 1500.3 GB, 1500299395072 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930272256 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0003e17f

    Device Boot      Start         End      Blocks   Id  System
/dev/sdg1            2048  2930272255  1465135104    7  HPFS/NTFS/exFAT
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Can you mount it manually on the system A? –  topr Sep 14 '12 at 12:00
    
Does any message about the device appear using dmesg? –  terdon Sep 14 '12 at 15:32
    
@tamashumi: I can't mount it on system A since it doesn't even appear as a device when I do sudo fdisk -l –  Menelaos Perdikeas Sep 14 '12 at 20:25
    
Unless you already had try different USB ports and cables on system the A. HDD is USB 3.0 or 2.0 compatible? Check on both systems what compatibility mode is set in BIOS for USB controller. You can check if there is no USB driver issue, but if other devices are connecting fine on system A it's less likely to be the reason. –  topr Sep 15 '12 at 13:06
    
@tamashumi. I updated my post with the output of tail -f /var/log/syslog when I plug the external HDD to a USB port of System A. I should mention that the HDD used to be visible and mountable on System A as well, it just stopped working after some time. I am wondering if this could point to a hardware malfunction after a crash. –  Menelaos Perdikeas Sep 15 '12 at 22:23

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