RAID Levels for Home NAS: Which Should You Choose?

4/24/2026 · Storage · 8 min

TL;DR

• RAID is not a backup — it protects against drive failure, not user error, ransomware, or fire
• For most 2-bay home NAS units, RAID 1 (mirror) is the right default — simple, fast to rebuild, easy to recover
• For 4+ bay units, RAID 6 or SHR-2 / RAID-Z2 is the safer pick once drives pass 8 TB because rebuild times stretch into days
• RAID 5 is increasingly risky on large modern drives — a second failure during rebuild is more likely than people think
• RAID 0 has no redundancy and should never be used for anything you care about
• Always pair RAID with a real 3-2-1 backup: three copies, two media, one off-site

What RAID actually does

RAID — Redundant Array of Independent Disks — combines multiple drives into one logical volume to improve uptime, capacity, or speed. The key word is uptime: a RAID array keeps your NAS reachable when a drive dies, so you can swap the failed disk without downtime or data loss. It does not protect you from accidentally deleting a folder, a buggy app overwriting files, malware encrypting the share, a power surge frying multiple disks at once, or the NAS being stolen.

If those scenarios sound far-fetched, talk to anyone who has lost data — they almost always involve one of them, not a single drive failure.

The levels you actually need to know

Vendor flavors like Synology SHR, QNAP's flexible volumes, and ZFS's RAID-Z1/Z2/Z3 map closely onto RAID 5/6 ideas but allow mixed drive sizes more gracefully.

RAID 0 — striping, no redundancy

Two or more drives are split into stripes and writes are spread across all of them. You get the full combined capacity and roughly N times the throughput of a single drive. The catch: if any drive dies, the whole array is lost. For a NAS that holds photos, documents, or media you would have to re-rip, this is almost never the right choice. Reserve it for scratch space — video editing caches, transcode buffers — that you can lose without consequence.

RAID 1 — mirroring

Two drives hold identical copies of your data. You lose half the raw capacity but gain the simplest possible redundancy: pull one drive, the other still works. Read performance can be a little better because the controller can pull from either disk; write performance matches a single drive. Rebuilds after a drive swap are straightforward and fast because they only have to copy from the surviving disk.

For a 2-bay home NAS — a Synology DS224+, QNAP TS-264, or similar — RAID 1 is the default for a reason. It's predictable, recoverable, and the math is easy.

RAID 5 — single parity

Spreads data and parity across three or more drives. With four 8 TB drives you get ~24 TB usable instead of the 16 TB you would get with RAID 10. One drive can fail without data loss. The downside is two-fold:

First, every write has to update parity, which slows write performance — especially for small random writes — unless your NAS has hardware acceleration or enough RAM cache.

Second, and more importantly, rebuilds on large drives are dangerous. Replacing a failed 12 TB drive in a 4-disk RAID 5 means reading every sector of the three surviving drives end-to-end. With consumer drives at typical bit-error rates and rebuild times of 12–48 hours, the chance of hitting an unrecoverable read error or a second drive failure during rebuild is no longer negligible. Many storage admins have stopped recommending RAID 5 for any drive larger than ~4 TB.

RAID 6 — double parity

Same idea as RAID 5 but with two parity blocks per stripe instead of one. Needs at least four drives. Two drives can fail simultaneously without data loss, which is the answer to RAID 5's rebuild-window problem. You give up another drive's worth of capacity (so 4×8 TB = ~16 TB usable, same as RAID 10) and writes are slower than RAID 5 because there are two parity calculations.

For a 4-bay or larger NAS holding drives ≥8 TB, RAID 6 (or SHR-2 or RAID-Z2) is the conservative, sensible default. The capacity hit is real but the second parity disk is what lets you sleep at night during a multi-day rebuild.

RAID 10 — striped mirrors

Two mirrored pairs striped together. Four drives minimum, 50% usable capacity. You get great read and write performance, and rebuilds only need to copy the surviving half of the broken mirror — so they're fast and put little stress on the rest of the array. The trade-off: you can survive any single drive failure, but if the second drive to fail is the partner of the first, you lose everything.

RAID 10 is the right pick when you need write performance — virtual machines, busy databases, heavy concurrent users — more than you need maximum capacity.

JBOD and single-drive volumes

Some NAS users run drives independently — one volume per disk — and use replication or backup software to copy critical data between them. This is appropriate when you mostly store cold archive data, want to spin down idle disks to save power, or plan to mix drive sizes that don't slot neatly into a RAID set. The downside is no automatic uptime: a dead drive means a dead share until you restore from backup.

SHR, RAID-Z, and other vendor variants

Synology Hybrid RAID and ZFS's RAID-Z family solve a real annoyance with classic RAID: mixed drive sizes. Plain RAID 5 with a 4 TB and a 6 TB drive treats both as 4 TB. SHR will use the extra 2 TB by carving the drives into multiple parity groups behind the scenes. If you expect to upgrade drives one at a time over years, vendor variants are usually worth the small loss of portability.

ZFS additionally gives you checksums on every block — silent bit-rot detection that traditional RAID does not provide. For long-term photo and video archives, that's a meaningful feature.

Rebuild times — the part most guides skip

Replacement is the moment when RAID earns or loses its keep. Rough numbers for a healthy NAS rebuilding to a fresh drive:

During a parity rebuild every surviving drive is being read continuously, often at lower priority than user I/O if the NAS is in use. That's both a stress test for the remaining drives and a window where a second failure is fatal in RAID 5. RAID 6 turns "fatal" into "uncomfortable but recoverable."

Practical picks by NAS size

• 2-bay, casual use (photos, documents): RAID 1. Easy, fast, reliable.
• 4-bay, mixed media and small backups: SHR-1 or RAID 5 if drives are small (≤4 TB) and you have current backups; RAID 6 / SHR-2 once any drive is ≥8 TB.
• 4-bay, performance-sensitive (Plex transcoding, VMs, dev work): RAID 10.
• 6+ bay, long-term storage: RAID 6 minimum; RAID-Z3 or two parity groups if you can spare the disks.
• Cold archive across mismatched drives: JBOD with replication to a second device or cloud.

Backup is still your job

Even RAID 6 with hot spares does not replace the 3-2-1 rule: three copies of the data, on two different media, with one copy off-site. A second NAS at a relative's house, a cloud target like Backblaze B2 or Wasabi, an encrypted USB drive in a safety-deposit box — pick the option you'll actually maintain. Versioned snapshots (Btrfs, ZFS, or Synology's snapshot feature) catch the everyday disasters — accidental delete, ransomware, software bug — that no RAID level can help with.

Bottom line

For a small home NAS, RAID 1 keeps things simple. For a four-bay or larger box with drives of 8 TB or more, RAID 6 or its vendor equivalents are worth the lost capacity for the rebuild safety they provide. Treat RAID 0 as scratch space only, treat RAID 5 as a legacy choice that's increasingly uncomfortable on modern drive sizes, and treat all RAID levels as uptime insurance — never as a substitute for a real, tested backup.

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