RAID (Redundant Array of Independent Disks) is one of the most misunderstood concepts in home storage. People assume RAID is a backup strategy. It isn’t. RAID is a way of combining multiple drives to either improve performance, add redundancy against drive failures, or both. Understanding the difference between RAID levels before building your home NAS can save you from losing data you thought was protected.
RAID 0: Speed Without Protection
RAID 0 stripes data across two or more drives — each file is split and written to multiple drives simultaneously, which improves read and write throughput. Two 4TB drives in RAID 0 give you 8TB of usable space and roughly 2x the sequential performance of a single drive.
The critical caveat: if either drive fails, all data on both drives is lost. RAID 0 actually increases your risk of data loss — with two drives instead of one, you have twice the probability of a failure. Never use RAID 0 for important data without a separate backup. Its use case is temporary scratch storage or video editing workspaces where speed matters and data can be regenerated.
RAID 1: Mirroring for Safety
RAID 1 mirrors data across two drives — every piece of data is written identically to both drives simultaneously. With two 4TB drives, you have 4TB of usable space (50% efficiency). If one drive fails, the other has all your data, and the array continues operating normally.
RAID 1 is the right choice for a small 2-drive NAS where data safety matters more than maximum capacity. It’s simple, well-understood, and natively supported in both TrueNAS and OpenMediaVault. The downside is inefficiency — you’re only using half your raw storage capacity for data.
RAID 5: The Home NAS Sweet Spot
RAID 5 stripes data and parity information across three or more drives. With three 4TB drives, you have 8TB of usable space (one drive’s worth used for parity). With four drives, you have 12TB usable. If any single drive fails, the array can reconstruct the lost data from the parity information on the remaining drives.
RAID 5 is the most popular choice for home NAS builds because it balances capacity efficiency, performance, and redundancy well. The minimum of three drives is a reasonable starting point, and you can expand by replacing drives with larger ones over time (with some NAS software supporting online capacity expansion).
The risk with RAID 5: during a rebuild after a drive failure, the remaining drives are under heavy sustained read load. If a second drive fails during reconstruction — which is more likely when drives are all the same age and workload — all data is lost. RAID 6 addresses this by using two parity drives, allowing two simultaneous failures, but requires a minimum of four drives.
RAID 6 and RAID 10
RAID 6 uses two parity blocks per stripe, surviving two simultaneous drive failures. With four 4TB drives, you get 8TB usable. Slower write performance than RAID 5 but meaningfully safer for large arrays where rebuild times stretch to days.
RAID 10 combines mirroring and striping — pairs of drives are mirrored, then striped across pairs. Excellent write performance and very fast rebuild times. Requires a minimum of four drives and uses 50% of capacity (same as RAID 1). The preferred choice when performance and reliability are both critical and capacity efficiency is secondary.
Important: RAID Is Not a Backup
RAID protects against hardware failure of a single drive. It does not protect against: accidental deletion, ransomware (which encrypts all drives simultaneously), fire, flood, or theft. If you delete a file on a RAID 5 array, it’s gone from all drives immediately.
The gold standard for data protection is the 3-2-1 rule: three copies of your data, on two different media types, with one copy stored off-site (cloud backup services like Backblaze B2 or Wasabi work well for this). RAID is one of those copies — not a substitute for the others.
FAQ
Can I do RAID with a mini PC? Yes. Software RAID through TrueNAS, OpenMediaVault, or mdadm on Linux works well on mini PC hardware. For a mini PC NAS using a USB dock with multiple shucked drives, software RAID via TrueNAS is the standard approach.
Does RAID slow down my NAS? RAID 1 has negligible performance impact. RAID 5 write performance is slightly lower than a single drive due to parity calculation. For home NAS workloads (media streaming, file access, backups), you will not notice the difference in practice.