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I have an external USB drive from LaCie that is connected to my MacBook Pro – almost all the time. So whenever I don't use it for a few minutes, it powers down. That means, it takes a few seconds to spin the disk up again if I need it.

Sometimes, other applications wake the drive up even when I don't want to, causing the applications to hang (i.e. wait for the drive).

How can I increase the time before the external drive powers down?

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May I ask which LaCie drive you have? I've heard quite a lot about LaCie and how Mac users like using them (With me being one of them), but I was dissuaded by the high costs of it so I used Western Digital instead. Do you like the drive? – JFW Mar 3 '11 at 16:12
I don't know which type it was. I bought it 2008 and it had a 500Gig SATA drive in it. The main reason it's used by Mac people is probably the design. The disk controller died last week and altoghether the disk wasn't particularly great. It was loud as hell. Stay with WD, they make good drives from my experience. – slhck Mar 3 '11 at 17:30
up vote 6 down vote accepted

Cocktail is an award winning general purpose utility for Mac OS X

This app does exactly what you are after (plus much much more), but it will set you back $15.

Alternatively, the command pmset appears to do this as well, but without the fancy GUI. For example pmset -c disksleep 60 will prevent all disks from spinning down within 60 minutes of activity when plugged in. You can change the -c part to specify a different power condition:

The -a, -b, -c, -u flags determine whether the settings apply to battery ( -b ), charger (wall power) ( -c ), UPS ( -u ) or all ( -a )

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+1 I really enjoy of learning 'pmset' – Am1rr3zA Sep 25 '10 at 17:26

Keep Drive Spinning is a free alternative that does what you want.

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The externals sleep routine is set by the drive's firmware. A few can respond to Energy Saver/Cocktail/pmset settings, most cannot. The only way to keep a drive is to have an app/script write to it at intervals. The video editing folks need this and their forums are where to look for answers.

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