Steven JW Kennedy

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The case of the missing disks

Posted by Steven Kennedy on January 19, 2011


I have a Mac Mini which has a 1.5TB external disk connected to it. Every now and then, I go to do something on my Mac and find that the disk is no longer mounted. I have un-plug the power and plug it back in which re-mounts the disk.

I’ve had a look around various forums but haven’t seen anything directly on point. Some stuff out there to do with AirPort Extreme, Time Capsule etc. but I’m not using either.

My actual setup is;

  • Mac Mini Dual Core 1.66GHz, 2GB RAM (model macmini1.1)

  • OS X 10.6.6

  • Boot ROM: MM11.0055.B08

  • External disk

  • Seagate FreeAgent 1.5TB

  • Partitioned in to two (2) partitions, 1TB and 500GB

  • The 1TB has iTunes and iPhoto files on it. the 500GB partition is used for files that I don’t use much. That is it’s not accessed on a regular basis.

  • Formatted MAC OS Extended (Journaled)

  • Direct USB cable from the Mac Mini to the Seagate

    When I encountered this issue in the past I went through a number of troubleshooting steps that included swapping out the USB cable and moving the disk from a USB hub to a direct connection to the Mac Mini. None of these ‘fixed’ the problem. This issue seems to come and go. It’s not something that I can reproduce at will so when I make a change, like swapping the USB cable I have to just wait to see if the problem re-occurs. The problem also seems to occur in groups. That is, it wont happen for a while, then it’ll reoccur and it’ll occur sporadically for a few days or a week or so and then go away.

    I have found the following in the system logs, but as far as I can tell it doesn’t tell me much, just that the disk, the 1TB partition, isn’t available.

    I did just look at the previous log entries, based on the time stamp of when I lost access to the external drive and notice that it seems to have a problem with a USB device plugged in to Port 6 of a USB hub.

    Which begs the question, how do I identify what device is plugged in to port 6. I do have a hub connected but it’s only a 4 port hub (powered). I have the following plugged in to the 4 port hub;

    1. ✦ Dell monitor, ie. another USB hub – nothing connected allows me to connect USB thumb drives via the monitor

    2. ✦ External disk drive, 2TB that I use for my backups

    3. ✦ USB hub, the Belkin hub with firewire that matched the Mac Mini, nothing plugged in to it.

    4. ✦ iPod USB cable – iPod wasn’t connected during this time

    Or does the Port 6 refer to the Mac Mini’s USB port, which would be odd as well as it doesn’t have 6 ports either. Having said that in looking at the information from the System Profiler and the log file it would seem that my USB High-Speed Bus has a Bus Number of 0xfd, the same prefix as is reported in the log, 0xfd600000. In addition the system profiler shows my Seagate as having a Location ID of 0xfd600000. So does this mean the prefix of 0xfd indicates the USB High-speed bus and the 6 indicates port 6? If so that would seem to point to the external Seagate disk as being the problem.

    I’ll keep plugging away at this to see if I can identify the cause of the problem. If I find anything then I’ll post a comment about it.

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