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I have an external USB hard drive I use for backing up my MacBook (running the latest Lion). FWIW, it's a Western Digital internal 3.5" SATA drive in an Antec HD enclosure. Anyway, of course every so often I have to unplug it so that I can take my MacBook places, so I eject the drive as usual and everything's cool.

But when I plug the drive back in, it doesn't mount. If I plug it in and then power-cycle the drive itself, then it mounts just fine, but due to how my office is laid out, this is inconvenient. And, too, I shouldn't have to power-cycle the drive, right? I should be able just to plug it in and have the MacBook recognize it, no?

So: what's going on and how can I fix it?

Thanks in advance for any and all help.

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What model is the Mac? What model is the drive? What model is the Antec HD? USB 2 or 3? Details, maybe with product IDs, from System Information will be ideal … thanks. – Graham Perrin Nov 1 '12 at 10:21

2 Answers

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There is a workaround, sometimes the drive will detect but not mount. If you open Disk Utility it should be listed on the sidebar and you can manually mount it from there.

This doesn't resolve the underlying issue of why OS X hasn't automounted, but if you check in the system logs when you plug it in you might get a clue towards that.

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Thanks for the idea, but sadly, that didn't do the trick: the drive doesn't appear in the sidebar. :( – Alex Basson Oct 28 '11 at 13:33
Poop! Do you get any mention of it in the syslogs? Or anything coming up to say it's not detected? I won't alarm you, but I've had this issue before and it was basically an early warning sign of disk issues, when you next get it to show do a First Aid check in Disk Utility. – Nicholas Smith Oct 28 '11 at 13:57
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Is drive plugged directly into the MacBook, or does it go through a hub? Sometimes hubs can cause funny recognition problems. – Wayfaring Stranger Feb 27 '12 at 19:57
up vote 1 down vote

The requirement to power the drive enclosure off, then (quickly) on, suggests to me that:

  • the drive does not spin up in good time
  • maybe the extra power required, for a timely spin up, is insufficient or too short.

If it were a LaCie drive, I would say try a new power supply.

Also, adapted from my answer about a random connection issue:

If the file system is dirty at time of connection of the disk, then the operating system will run fsck_hfs until (hopefully) repairs seem to succeed. During this period the volume will be not mounted, and the OS presents no alert.

(An alert appears only if, for example, repairs are unsuccessful.)

For a file system that includes backups written by Time Machine: if repairs are necessary, fsck_hfs may take an extraordinarily long time.

With Console you can browse

/var/log/fsck_hfs.log

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