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I've purchased a bracket to replace the superdrive in my 2009 Unibody MBP, the kind with the latch that pops open rather than the entirely screwed down bottom panel.

Now that I've put in my second hard drive, the drive constantly has to spin up when I stop using it for any seriously length of time. I presume this is meant as a power-saving measure for the old superdrive.

Is there any way to disable this behavior, and have the drive powered on at all times? While I'm not eager to punish my battery, I've pretty much worn my battery down to nothing by now, so I'm quite used to having my laptop plugged in at all times.

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Have you set your power settings to "power off disks when possible"? – Thorbjørn Ravn Andersen Aug 27 '12 at 19:03

Run sudo pmset disksleep 0, with an optional -a, -b, -cor -u between the pmset and the disksleep.

See man pmset for details:

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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can I set it to just the individual disk? – Alex Aug 27 '12 at 21:13
AFAIK, no, it's a system-wide setting. – Daniel Serodio Aug 28 '12 at 13:06

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