TL;DR — Quick Summary
Choose the right RAID level for your needs: RAID 0, 1, 5, 6, 10, and 50 compared by performance, redundancy, capacity, and use case. Includes hardware vs software RAID and SSD considerations.
Choosing the Right RAID Level
RAID (Redundant Array of Independent Disks) combines multiple physical drives into a single logical unit for performance, redundancy, or both. Choosing the correct RAID level is one of the most important decisions for any server storage design.
RAID Level Comparison
| RAID | Min Disks | Usable Capacity | Read Speed | Write Speed | Fault Tolerance | Rebuild Risk |
|---|---|---|---|---|---|---|
| 0 (Stripe) | 2 | 100% | ⚡ Fastest | ⚡ Fastest | ❌ None | N/A |
| 1 (Mirror) | 2 | 50% | ✅ Fast | ✅ Normal | 1 disk | Low |
| 5 (Stripe + Parity) | 3 | (N-1)/N | ✅ Fast | ⚠️ Slower | 1 disk | ⚠️ High (large drives) |
| 6 (Stripe + 2 Parity) | 4 | (N-2)/N | ✅ Fast | ⚠️ Slow | 2 disks | Moderate |
| 10 (Mirror + Stripe) | 4 | 50% | ⚡ Fastest | ✅ Fast | 1 per mirror | Low |
| 50 (Stripe of RAID 5) | 6 | (N-G)/N | ⚡ Fast | ⚠️ Moderate | 1 per sub-array | Moderate |
Capacity Examples (8 × 4TB Drives)
| RAID | Usable | Lost to Redundancy |
|---|---|---|
| 0 | 32 TB | 0 TB |
| 1 | 16 TB | 16 TB |
| 5 | 28 TB | 4 TB |
| 6 | 24 TB | 8 TB |
| 10 | 16 TB | 16 TB |
When to Use Each RAID Level
RAID 0 — Maximum Performance, Zero Protection
- ✅ Video editing scratch disks, temp data, caches
- ✅ Workloads where data can be recreated from backups
- ❌ Never for anything you can’t afford to lose
RAID 1 — Simple Mirroring
- ✅ OS drives, boot drives
- ✅ Small servers with 2 drives
- ✅ Simple, fast rebuild
RAID 5 — Balanced (Caution with Large Drives)
- ✅ File servers, NAS with 3-4 drives under 4TB each
- ⚠️ Risky with large drives (8TB+) — rebuild can take 24+ hours
- ⚠️ During rebuild, a 2nd failure = total data loss
RAID 6 — Safer Parity
- ✅ File servers with large drives (8TB+)
- ✅ NAS arrays with 4+ drives
- ✅ Survives 2 simultaneous drive failures
RAID 10 — Best for Databases
- ✅ Database servers (SQL, MySQL, PostgreSQL)
- ✅ Virtualization hosts (VMware, Proxmox, Hyper-V)
- ✅ High-write workloads
- ✅ Fastest rebuild time
Hardware RAID vs. Software RAID
| Aspect | Hardware RAID | Software RAID |
|---|---|---|
| Cost | $200-$1000+ for controller | Free (built-in) |
| Write cache | ✅ Battery-backed (BBU) | ❌ (unless ZFS with SLOG) |
| CPU usage | Offloaded to controller | Uses host CPU |
| Portability | ❌ Locked to controller brand | ✅ mdadm/ZFS move between systems |
| SSD optimization | ❌ Often poor TRIM support | ✅ Full TRIM support |
| Recommended for | Enterprise databases | Most modern servers, NAS |
Tip: If using SSDs or NVMe, software RAID (ZFS, mdadm, or btrfs) is usually better than hardware RAID because it supports TRIM and doesn’t have controller lock-in.
The 3-2-1 Backup Rule
RAID is not a backup strategy. Always follow:
- 3 copies of your data
- 2 different storage media (e.g., local + cloud)
- 1 offsite copy (cloud backup, different location)