NAS RAID should be selected around the number of drives, capacity requirements, performance requirements and acceptable failure scenarios.
Practical example: choosing RAID for a file server
RAID availability and backup recovery solve different problems.
Scenario: A business file server needs usable capacity, reasonable write performance and tolerance for a drive failure.
RAID 0 would provide no redundancy, so it is unsuitable for this requirement. RAID 1 is simple but uses half of the raw capacity for mirroring. RAID 5 and RAID 6 introduce parity and different failure-tolerance and write-performance trade-offs. RAID 10 combines mirroring and striping but also has a significant capacity overhead.
Decision: Choose the RAID level from the workload, number of drives, rebuild risk, usable-capacity requirement and controller support. Then create a separate backup because RAID does not protect against deletion, corruption, malware or loss of the entire server.
Common mistakes and selection checklist
Common mistakes
- Selecting RAID only from the amount of usable capacity it provides.
- Ignoring rebuild time, drive count, write workload and the consequences of another drive problem during recovery.
- Treating RAID as a backup.
What happens if you get it wrong?
The array may have the wrong performance or resilience characteristics for the workload. A controller, corruption, deletion, malware event or complete system loss can still make the data unavailable even when the RAID level itself is working as designed.
Selection checklist
- Define the usable-capacity target and workload before selecting a RAID level.
- Check the minimum and practical drive count for the chosen layout.
- Consider write behaviour, rebuild exposure and failure tolerance.
- Verify controller, drive and server-platform support.
- Maintain a separate tested backup and recovery process.
A resilient array keeps services available during some drive failures. Separate backups provide recovery from deletion, corruption, malware and site loss.
RAID 0
RAID 0 stripes data across drives and provides no redundancy. It is generally unsuitable for important data where drive failure must be tolerated.
RAID 1
RAID 1 mirrors data between drives and provides redundancy, but only part of the raw drive capacity is available as usable storage.
RAID 5
RAID 5 uses parity and can tolerate one drive failure. It provides more usable capacity than mirroring but has different performance and rebuild considerations.
RAID 6
RAID 6 uses dual parity and can tolerate two drive failures in the array, at the cost of additional capacity for parity.
RAID 10
RAID 10 combines mirroring and striping and can provide strong performance and redundancy, but requires additional drives.
RAID is not backup
RAID protects against certain hardware failures. It does not protect against accidental deletion, corruption, malware, theft or every other cause of data loss.
Capacity, drive count, rebuild requirements and the importance of the data should all be considered before choosing a configuration.
Confirm the exact product specification, supported configuration and compatibility before ordering. Platform generation, firmware, licences and optional components can change what a product supports.