"The marketing droids would have you believe that RAID is an answer to all of your storage wrongs. Bullshit. The most common cause of drive failure in modern enclosures is heat. When multiple drives share an enclosure, they tend to fail about the same time. We experienced this on Friday night, when two drives died within about 3 hours late one night."

Thankfully, they were making incremental backups to a separate server via rsync. Read the link above for the details.