Maybe the disk is faulty. There is literally nothing on the disk. I formatted it and put nothing on it, and it's spinning constantly, with a faint clicking noise. The HD's activity light never blinks, indicating there is no activity. This is the product. According to the reviews, it is famous for being quiet, and for me I can clearly hear it quiet loudly, and it's still annoying when watching videos or listening to music so clearly I'm not experiencing the same thing that other reviewers are.
You can do this using the "Spindown HD" program that came with older versions of the OS X developer tools: http://reviews.cnet.com/8301-13727_7-20070163-263.html
For a similar approach, you can set the power manager to spin down the hard disks at a given time between 1 minute and up to whatever number of minutes you would like, using the following command:
sudo pmset -a disksleep MINUTES
If you set MINUTES to 0 then the disks will never spin down, and MINUTES must be an integer value so you cannot specify 30 seconds or other fractions of a second.
You may be dealing with the problem that the OS itself (or its apps) like to randomly read stuff off every hard drive when it's bored. At one point I tracked my OS's disk access activity, and sure enough, Finder banged another external drive about every 5-10 minutes in round robin. This was 10.5 so maybe they fixed this.
Some programs also scan all your drives looking for resources, and once they find it on an external drive, they will continue looking there forever, even if you delete the folder. I suppose you could rename the external drive. For instance, my system believed that 3 of my fonts were located on external drives, so everytime I opened a Font menu, I would get a beachball for 10 seconds while the drive spun up. I was able to mess around in Font Book and make it stop doing that. Same thing when I start Word, which apparently has a prurient interest in "Word Settings" folders on my backup drives.
You can see what files it's getting on external drives by doing (at Terminal)
sudo fs_usage -f filesys | grep /Volumes/ and then it'll pop up everytime something goes to an external drive.
Note that this is a considerable resource-hog, so I don't run it when I am not actively using it.
To this day, everytime I go to an "open" or "save as..." menu, again, beachball for 20 seconds as every drive spins up one at a time. I don't think there's a way around that one.
These are commonplace external hard drives bought at CostCo, not some gold-plated "designed for Mac" specialty product. They do indeed spin down when nobody is using them.
I have chased my tail for YEARS on this problem, for instance I finally got the Fonts problem resolved (I think), but every problem I solve, two more pop up. I have just given up, and everytime I get a beachball I throw another dollar into the "buy solid state drives" fund.
This is the drive:
LaCie Minimus 2 TB USB 3.0 Desktop External Hard Drive 301967
Which comes with a package of LaCie Software. If it is setup for USB 3.0 do you meet the requirements including USB 3.0 PCI Express card? LaCie software also has backup and energy saver software. Are they set up?
I have no experience using new LaCie software. I've always set up drives thorugh the OS. Yours came semi setup since all the documentation is installed on the HD/