RAID 5 vs RAID 6
This guide supports the Storage Calculators shelf by explaining the decision behind the calculator. Calculator pages give you the number; guides help you understand when the number is good enough and when a different setup is safer.
What this guide covers
RAID 5 gives more usable space, while RAID 6 gives dual-parity protection during rebuild risk. The practical goal is to choose storage with enough usable capacity, enough failure tolerance, and enough headroom for growth without pretending that one formula fits every device or workload.
Decision checklist
- Define the usable capacity you actually need.
- Choose whether redundancy, speed, cost, or simplicity matters most.
- Account for hot spares, filesystem overhead, decimal-vs-binary units, and backup needs.
- Compare at least two scenarios with the calculators before buying hardware.
When RAID 5 makes sense
RAID 5 is usually the capacity-first option for smaller arrays with reliable backups, replaceable data, and a tolerance for one-drive fault protection. It keeps more usable space because only one active drive is reserved for parity.
When RAID 6 is safer
RAID 6 is usually the safer choice for larger disks, longer rebuild windows, colder archives, or any array where a second drive failure during rebuild would be costly. The tradeoff is lower usable capacity because two active drives are reserved for parity.
Worked comparison
With six 12 TB drives and no hot spare, RAID 5 provides about 60 TB before overhead while RAID 6 provides about 48 TB before overhead. The extra 12 TB from RAID 5 is useful only if the lower fault tolerance is acceptable and a separate backup exists.
Related calculators
- Disk RAID Calculator Interactive calculator
- NAS Capacity Calculator Interactive calculator
- Surveillance Storage Calculator Interactive calculator
- Download Time Calculator Interactive calculator