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Why does OS X insist on spinning up all the attached external drives (firewire, usb) when loading a file from the local (internal) drive?

It's driving me insane that I have to wait for 3 attached drives (1 back-up, 2 media) to spin up -- a total of 20s -- to access a file that is located only on my local/internal drive. There is no obvious need to access the other drives; nothing is being read from them and nothing need be written.

Examples: Quicktime X opening a file from the local HDD. Starting Caffeine, an app which doesn't access any other files at all.

Can I tell OS X to only spin those drives up when actually accessing them?

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good question. I never have a DVD in the drive for just this reason. –  Yar Mar 2 '10 at 15:30

4 Answers 4

If by "access" you mean perform I/O operations on a file, then that should not be happening. If by "access" you mean that you're bringing up the standard Open/Save dialogs, then you are actually hitting those filesystems whether you realize it or not.

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My guess is that it's not the file-read itself, but related actions. Maybe it's querying available disks (in case you want to Save As), or checking references to recently-used files, etc. Essentially the software is doing a lot more in the background than "loading the file you asked."

I'll admit I don't know anything about Caffeine, but maybe since its purpose is to stop things from going to sleep, it's intentionally waking up the HDs?

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Caffeine stops the screen from dimming, which is useful when watching flash videos in full-screen (such as programs on the BBC-iPlayer). Since it's only purpose is to stop the screen dimming it shouldn't access any disks, and being a single file it doesn't need to load anything other than itself. –  Phillip Oldham Mar 6 '10 at 9:44

Sadly the operating system automatically presents all possible data sources which does not work well for externally attached media that is not accessed regularly.

It's kind of like looking at a car at a dealer. You can either take the dealers word for it that there is a blue one out in the lot or you can walk out there and take a look yourself.

I have questioned this with Apple support and been told tough luck.

One day maybe they will have the intelligence to a only present possible data sources initially rather than actually probing all available devices which causes them to spin up.

The problem will pretty much go away with solid state drives which have almost instant on access.

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Yet another guess here.

Maybe it's something you've installed / configured. I've never tried this before, but I would reboot into safe mode (by holding shift along with the booting sound) and see if the problem still happens.

Then it would be an extensive job looking for what could be doing that. If your memory fails, I'd start with the Console and see what's there right in the moment the issue happens.

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