This has happened to me for as long as I have used Macs, I think.

Occasionally, Mac OS X remembers a long-forgotten disk, sometimes external, sometimes internal, and spins it up for some reason. And every time this happens, the front-most application, the one I am using at that moment, hangs until the disk has spun up.

Why does that happen and can I tell OS X that the application in focus ought to have priority over hard disks? (Note that it is not the boot hard disk with the swap file that is being spun up.)

  • Are you asking it to look up for something.
    – Ruskes
    Apr 12, 2013 at 23:43
  • No. In fact all my applications are located on the boot disk and wouldn't typically access the other disks. It's Boot Camp using an external disk very often. Apr 13, 2013 at 0:30
  • It is difficult to answer your question without more details.
    – Ruskes
    Apr 13, 2013 at 7:53
  • @AndrewJ.Brehm - Does it only happen when you access a hard drive at all (i.e. saving, opening a file, etc.) or does it just happen spontaneously while using it? I've only had it happen when I go to open a file load/save dialog.
    – Bobson
    Sep 23, 2013 at 22:02
  • It usually happens when a save file dialogue comes up. Sometimes it happens at a seemingly random moment and just makes me wait five seconds for no apparent reason. Sep 24, 2013 at 6:53

2 Answers 2


I know exactly what you mean Mine does it with my external HD

It drives me nuts. I've replaced my HD in my MBP with a SSD. I've been thinking about replacing the SuperDrive with a hard drive tray and putting the original drive in it, but if my computer is going to hang to spin up the HHD it isn't worth it.

I guess I just have to buy one, install it, and see what happens. I'll let you know Tuesday when the caddy tray arrives if it is an OS-HD issue, or a OS-USB issue

  • 1
    I always end up regretting my decision to allow spinning drives to sleep. It's nice to have externals spin down, but the lag of an internal sleeping is no fun at all.
    – bmike
    Sep 23, 2013 at 16:26

I don't have an authoritative answer, but my impression is that it needs to spin up the drive in order to access some metadata from it (name, size, capacity, or similar), or simply to check that it's still there.

There is a 7 page thread on the Apple forums about this, with some suggestions but no hard solutions. Ditto for this Superuser.SE question.

The only real solutions appear to be to either A) Prevent the drive from going to sleep, or B) unmount the drive until needed.

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