I’m always amused when I come across proof that long-held assumptions in the tech world are wrong. Today’s amusement comes from the Battle Against Any RAID {Four,Five}, aka, BAARF. These guys have been down on parity setups since June of 2003, back when 120 GB drives were HUGE. They even have a good writeup of RAID5 vs RAID10. The tl;dr version is: RAID5 is almost never worth it for anything high-end, and RAID5 isn’t as reliable as you think. Considering the number of times I’ve seen standalone RAID5 arrays lose all data… yeah, not so much.

This is backed up by other, less inflammatory people. Robin Harris, StorageMojo wrote about the usable lifetimes of RAID5 and RAID6. Google has put out an academic paper on the topic of Unrecoverable Read Errors making RAID less and less useful as time goes by.

If you’re using RAID5 as primary storage, make sure you have good backups.