Today, during my surfing threw the web I came across an interesting tid bit.
A fairly high class installation of a networked media system in a house. They've invested a few 10k EUR I can imagine. And they did not go RAID.
The stated reason was, running all disks the whole time stresses all disks identical. This results in the same fatigue for all disks, and quite probable make them fail at the same time.
Instead, they opted for a simple NAS doing backups at night. During the day, the HDD in the NAS are kept powered down.
With todays prices for storage, this might be a worthwhile idea for LinuxMCE users as well.