Will spinning down hard disks create Linux Raid problems?

I've done this with a Linux raid-5 array, and never had any trouble from it sync-wise. There was a noticeable lag when the drives would spin up, about 45 seconds or so. Power-wise, though, I've decided it wasn't really worth it. The server consumed 90 watts when the drives were spinning (it was build with power consumption in mind), and 70 when they were spun down. That difference didn't justify the wait time from spinning them back up.

I've done this before (5+ years ago) and never saw any problems with spinning down the disks. Unless the disk doesn't spin back up, it should be ok. Your access times will suffer though. Pick a good spin-down time - something that will keep the disks spun up during the time you'll use them. I chose 15 minutes. It was generally good during use, and when I stopped using the disks (overnight for example) it spun down soon enough.

I don't know what kind of power savings you'll get - I spun down disks to cut down on noise. I wasn't using the best disks...