RAID 5 Capacity Calculator
Calculate usable storage in a RAID 5 array. See exactly how much space you lose to parity and what you get for data.
✓ (N-1) × drive size formula
✓ Parity overhead breakdown
✓ Rebuild risk guidance
Distributes parity across all drives. Survives one drive failure. Good balance of capacity and protection.
Usable Capacity
11.82 TB
75.0% storage efficiency
RAID level comparison
| Level | Min | Fault tolerance | Capacity formula |
|---|---|---|---|
| RAID 0 | 2 | None | N × Size |
| RAID 1 | 2 | N−1 drives | 1 × Size |
| RAID 5 | 3 | 1 drive | (N−1) × Size |
| RAID 6 | 4 | 2 drives | (N−2) × Size |
| RAID 10 | 4 | 1/mirror pair | (N÷2) × Size |
| RAID 50 | 6 | 1/sub-array | (N−2) × Size* |
| RAID 60 | 8 | 2/sub-array | (N−4) × Size* |
| JBOD | 1 | None | N × Size |
| SHR | 1 | 1 drive (SHR-1) | ≈(N−1) × Size |
* Assumes 2 sub-arrays. N = number of drives.
Understanding RAID 5 Capacity
RAID 5 distributes parity data across all drives, providing single-drive fault tolerance with good capacity efficiency. It's the most popular RAID level for business storage.
The Formula
Usable Capacity = (N - 1) × Drive Size
3 × 4TB: (3-1) × 4 = 8TB usable (67% efficiency)
4 × 4TB: (4-1) × 4 = 12TB usable (75% efficiency)
6 × 4TB: (6-1) × 4 = 20TB usable (83% efficiency)
8 × 4TB: (8-1) × 4 = 28TB usable (88% efficiency)
RAID 5 Pros & Cons
- ✓ Good capacity efficiency: Only 1 drive worth of parity overhead
- ✓ Single drive fault tolerance: Survives any one drive failure
- ✓ Good read performance: Reads stripe across all drives
- ✗ Slow writes: Every write requires parity calculation and write
- ✗ Long rebuild times: 12–48+ hours for modern large drives
- ✗ Vulnerable during rebuild: A second drive failure during rebuild = total data loss
When to Choose RAID 5
RAID 5 is ideal for read-heavy workloads with 3–6 drives where capacity efficiency matters. File servers, media streaming, and archival storage are common use cases.
⚠️ Rebuild Risk Warning
With 8TB+ drives, RAID 5 rebuild can take 24–48 hours. During this window, a second drive failure destroys all data. For drives over 4TB, strongly consider RAID 6 (dual parity) instead.