A while back i decided to setup a 3-drive ZFS pool in the MacPro. The only complaint so far is that OS X gets a little eager with putting the drives to sleep for my taste. In more recent versions of OS X the only option for putting the drives to sleep is a checkbox that, when on, will attempt to put the drives to sleep after 10 minutes of inactivity.
In the early days of OS X the Energy Saver preferences looked a little different – users could set a time to wait before putting drives to sleep.
Thankfully after some digging i realized it could all be set through the pmset command. The man page has everything you need but for the lazy here’s the gist for disk sleep timing. pmset takes a flag to determine which power profile you’re changing: wall-charger (-a), battery (-b), UPS (-u) or all profiles (-a). Next simply pass it the disksleep argument and a number in minutes.
Set all power profiles to sleep the disks after 15 minutes instead of the typical 10:
sudo pmset -a disksleep 15
Setting the time to 0 will disable disk sleep altogether for that power profile.
One interesting thing to note is i originally stumbled onto this on a rather old article that suggested using the spindown argument instead of disksleep as the man page now suggests (as of 10.4). Using spindown does not cause pmset to complain though it appears to disable disk sleep altogether.