How Much RAID Redundancy Do You Actually Need? A Data Hoarder's Guide
Updated Aug 12, 2026: added ZFS-vs-traditional-RAID comparison, a rebuild-risk worked example, and a monitoring checklist. “RAID is not a backup” gets repeated so often it’s lost meaning. Here’s the version that actually helps you pick a redundancy level instead of just feeling vaguely guilty about your array. What redundancy actually protects against Redundancy (RAID-Z1, RAID-Z2, mirrors, whatever flavor) protects against drive failure, full stop. It does not protect against: Accidental deletion (redundancy dutifully replicates your mistake) Ransomware or file corruption that writes bad data (same problem) Fire, theft, flooding, or anything that takes out the whole box at once Controller or power supply failure that kills multiple drives simultaneously That’s what backups are for, and it’s a separate problem from redundancy. This post is specifically about the “how many drives can I lose without losing data” question. If you only take one thing from this post, take the 3-2-1 rule for the data you actually care about: 3 copies, on 2 different types of media, with 1 copy off-site. Redundancy is not one of the three copies - it just keeps your primary copy available while a drive is being replaced. ...