Quick Answer+
Quick Calculation: Use our free RAID calculator below to instantly calculate usable storage. A 4-drive array with 8TB drives in RAID 5/SHR gives 24TB usable (75% efficiency). RAID 6/SHR-2 gives 16TB (50% efficiency) with 2-drive protection. Enter your configuration for exact results.
Free RAID Calculator
Calculate usable storage capacity for any RAID configuration. Our RAID calculator supports Synology SHR, traditional RAID levels, and provides drive recommendations with current pricing.
RAID Types Explained
SHR
Synology Hybrid RAID. Flexible RAID that allows mixed drive sizes. 1-drive fault tolerance. Best for most users.
SHR-2
2-drive fault tolerance version of SHR. Recommended for 6+ drive arrays or critical data storage.
RAID 5
Single parity striping. Same capacity as SHR with identical drives. 1-drive fault tolerance. Minimum 3 drives.
RAID 6
Dual parity striping. 2-drive fault tolerance. Recommended for large arrays with big drives. Minimum 4 drives.
RAID 10
Striped mirrors. Best read/write performance with 50% capacity. 1-drive per mirror pair tolerance. Minimum 4 drives.
RAID 0
No redundancy! Any single drive failure = total data loss. Only use for temporary, non-critical data.
How to Use This RAID Calculator
- Select number of drives — Choose how many hard drives in your array (2-12)
- Select drive capacity — Choose the size of each drive (2TB-24TB)
- Select RAID type — Choose your RAID level (SHR, RAID 5, RAID 6, etc.)
- Click Calculate — Get instant results including usable capacity, efficiency, and fault tolerance
RAID Calculator Quick Reference Tables
Don’t want to use the calculator? Here are pre-calculated results for common configurations:
RAID 5 / SHR Calculator Results
RAID 5 and Synology SHR provide single-drive fault tolerance with the same usable capacity formula: (N-1) × Drive Size
| Drives | Drive Size | Raw Capacity | Usable (RAID 5/SHR) | Efficiency |
|---|---|---|---|---|
| 3 | 8TB | 24TB | 16TB | 67% |
| 4 | 8TB | 32TB | 24TB | 75% |
| 5 | 8TB | 40TB | 32TB | 80% |
| 6 | 8TB | 48TB | 40TB | 83% |
| 4 | 12TB | 48TB | 36TB | 75% |
| 4 | 16TB | 64TB | 48TB | 75% |
| 6 | 12TB | 72TB | 60TB | 83% |
| 8 | 16TB | 128TB | 112TB | 88% |
RAID 6 / SHR-2 Calculator Results
RAID 6 and Synology SHR-2 provide two-drive fault tolerance: (N-2) × Drive Size
| Drives | Drive Size | Raw Capacity | Usable (RAID 6/SHR-2) | Efficiency |
|---|---|---|---|---|
| 4 | 8TB | 32TB | 16TB | 50% |
| 5 | 8TB | 40TB | 24TB | 60% |
| 6 | 8TB | 48TB | 32TB | 67% |
| 8 | 8TB | 64TB | 48TB | 75% |
| 6 | 12TB | 72TB | 48TB | 67% |
| 8 | 16TB | 128TB | 96TB | 75% |
RAID 10 Calculator Results
RAID 10 (striped mirrors) provides the best performance with 50% capacity: N/2 × Drive Size
| Drives | Drive Size | Raw Capacity | Usable (RAID 10) | Efficiency |
|---|---|---|---|---|
| 4 | 8TB | 32TB | 16TB | 50% |
| 6 | 8TB | 48TB | 24TB | 50% |
| 8 | 8TB | 64TB | 32TB | 50% |
| 4 | 16TB | 64TB | 32TB | 50% |
| 8 | 16TB | 128TB | 64TB | 50% |
RAID 1 Calculator Results
RAID 1 (mirror) is ideal for 2-drive NAS systems with full redundancy:
| Drives | Drive Size | Raw Capacity | Usable (RAID 1) | Efficiency |
|---|---|---|---|---|
| 2 | 4TB | 8TB | 4TB | 50% |
| 2 | 8TB | 16TB | 8TB | 50% |
| 2 | 12TB | 24TB | 12TB | 50% |
| 2 | 16TB | 32TB | 16TB | 50% |
| 2 | 20TB | 40TB | 20TB | 50% |
RAID Calculator Formulas
Understanding how RAID capacity is calculated helps you plan storage effectively. Here are the formulas used by our RAID calculator:
RAID Level Capacity Formulas
| RAID Level | Formula | Example (4×8TB) | Min Drives |
|---|---|---|---|
| RAID 0 | N × Size | 32TB (100%) | 2 |
| RAID 1 | Size | 8TB (25%) | 2 |
| RAID 5 / SHR | (N-1) × Size | 24TB (75%) | 3 |
| RAID 6 / SHR-2 | (N-2) × Size | 16TB (50%) | 4 |
| RAID 10 | (N/2) × Size | 16TB (50%) | 4 |
Where: N = Number of drives, Size = Capacity of smallest drive
Manual RAID Calculation Examples
RAID 5 with 5× 12TB drives:
Usable = (5 - 1) × 12TB = 4 × 12TB = 48TB Efficiency = 48TB ÷ 60TB = 80% Parity overhead = 12TB (1 drive equivalent)RAID 6 with 8× 16TB drives:
Usable = (8 - 2) × 16TB = 6 × 16TB = 96TB Efficiency = 96TB ÷ 128TB = 75% Parity overhead = 32TB (2 drive equivalent)RAID Types Explained
Choosing the right RAID level depends on your priorities: capacity, performance, or data protection. Here’s what each RAID type offers:
RAID 0 (Stripe) — Maximum Capacity, No Protection
- Capacity: 100% of total drives
- Fault tolerance: None — any drive failure loses ALL data
- Performance: Best read/write speeds
- Use case: Scratch disks, temporary files, non-critical data
- Recommendation: Not recommended for important data
RAID 1 (Mirror) — Simple Redundancy
- Capacity: 50% of total drives
- Fault tolerance: 1 drive (or half of drives in larger arrays)
- Performance: Good read performance, standard write
- Use case: 2-bay NAS, critical system drives
- Recommendation: Best for 2-drive configurations
RAID 5 — Balanced Performance and Protection
- Capacity: (N-1) drives worth — 75% with 4 drives
- Fault tolerance: 1 drive failure
- Performance: Good read, moderate write
- Use case: General NAS storage, file servers
- Recommendation: Great for 3-5 drive arrays
RAID 6 — Enhanced Protection for Large Arrays
- Capacity: (N-2) drives worth — 67% with 6 drives
- Fault tolerance: 2 simultaneous drive failures
- Performance: Good read, slower write than RAID 5
- Use case: Large arrays, critical data, enterprise
- Recommendation: Recommended for 6+ drive arrays
RAID 10 — Maximum Performance with Redundancy
- Capacity: 50% of total drives
- Fault tolerance: 1 drive per mirror pair
- Performance: Best overall performance
- Use case: Databases, VMs, high-performance applications
- Recommendation: When performance is priority
SHR (Synology Hybrid RAID) — Flexible RAID 5
- Capacity: Same as RAID 5 with same-size drives
- Fault tolerance: 1 drive failure
- Unique feature: Allows mixed drive sizes
- Use case: Synology NAS, home/SMB users
- Recommendation: Best choice for most Synology users
SHR-2 (Synology Hybrid RAID 2) — Flexible RAID 6
- Capacity: Same as RAID 6 with same-size drives
- Fault tolerance: 2 drive failures
- Unique feature: Allows mixed drive sizes
- Use case: Large Synology arrays, critical data
- Recommendation: Best for 6+ drive Synology NAS
RAID Comparison Chart
| RAID Type | Min Drives | Efficiency | Fault Tolerance | Read Speed | Write Speed | Best For |
|---|---|---|---|---|---|---|
| RAID 0 | 2 | 100% | None | ★★★★★ | ★★★★★ | Temp files |
| RAID 1 | 2 | 50% | 1 drive | ★★★★☆ | ★★★☆☆ | 2-bay NAS |
| RAID 5/SHR | 3 | 67-90% | 1 drive | ★★★★☆ | ★★★☆☆ | Most users |
| RAID 6/SHR-2 | 4 | 50-75% | 2 drives | ★★★★☆ | ★★☆☆☆ | Large arrays |
| RAID 10 | 4 | 50% | 1 per pair | ★★★★★ | ★★★★☆ | Databases |
Which RAID Should I Choose?
Use this decision guide to select the right RAID level:
| Your Situation | Recommended RAID | Why |
|---|---|---|
| 2-bay NAS | RAID 1 or SHR | Only options with redundancy |
| Home user, 4-bay NAS | SHR or RAID 5 | Good balance of capacity and protection |
| Plex/Media server | SHR or RAID 5 | Maximize storage for media files |
| Small business | SHR-2 or RAID 6 | Extra protection for business data |
| 6+ drive array | SHR-2 or RAID 6 | Long rebuild times need 2-drive protection |
| Database server | RAID 10 | Best random I/O performance |
| Surveillance system | SHR or RAID 5 | Sequential writes, capacity priority |
| Temporary/scratch files | RAID 0 | Maximum speed, data is replaceable |
RAID Calculator for Different NAS Brands
While our calculator is optimized for Synology, the RAID calculations work for any NAS brand:
Synology RAID Calculator
Synology supports SHR, SHR-2, and all standard RAID levels. Our calculator includes Synology’s unique SHR modes which allow mixed drive sizes.
QNAP RAID Calculator
QNAP uses standard RAID levels. Use RAID 5 calculations for their systems. QNAP doesn’t have SHR equivalent — use JBOD for mixed drives.
ASUSTOR RAID Calculator
ASUSTOR supports standard RAID levels similar to QNAP. The same RAID 5/6/10 formulas apply.
TrueNAS / FreeNAS RAID Calculator
TrueNAS uses ZFS with RAID-Z levels. RAID-Z1 ≈ RAID 5, RAID-Z2 ≈ RAID 6, RAID-Z3 = 3-drive parity. Same capacity formulas apply.
Unraid Calculator
Unraid uses a unique parity system. Single parity = similar to RAID 5 capacity. Dual parity = similar to RAID 6 capacity.
Frequently Asked Questions
RAID 5 capacity = (Number of drives – 1) × smallest drive size. For example, 4× 8TB drives in RAID 5 = (4-1) × 8TB = 24TB usable. One drive’s worth of capacity is used for parity data that enables recovery from a single drive failure.
RAID 5 uses single parity (1 drive fault tolerance), while RAID 6 uses dual parity (2 drive fault tolerance). RAID 5 formula: (N-1) × size. RAID 6 formula: (N-2) × size. RAID 6 is recommended for large arrays (6+ drives) because rebuild times are longer and risk of second failure increases.
SHR (Synology Hybrid RAID) is Synology’s flexible RAID system. It provides the same capacity and protection as RAID 5 but allows mixing different drive sizes. SHR automatically optimizes storage when you add larger drives. SHR-2 is the equivalent of RAID 6 with 2-drive fault tolerance.
Storage loss depends on RAID level: RAID 1 loses 50%, RAID 5 loses 1 drive’s worth (25% with 4 drives), RAID 6 loses 2 drives’ worth (33% with 6 drives), RAID 10 loses 50%. This ‘lost’ capacity provides data protection through redundancy.
RAID 5 or SHR is best for most NAS users. It offers a good balance of usable capacity (75%+ with 4 drives) and data protection (survives 1 drive failure). For critical data or large arrays (6+ drives), use RAID 6 or SHR-2 for two-drive fault tolerance.
No, RAID 0 provides NO data protection. If any single drive in a RAID 0 array fails, ALL data is permanently lost. RAID 0 should only be used for temporary files, scratch disks, or data that exists elsewhere. Never use RAID 0 for important files.
Traditional RAID (5, 6, 10) requires same-size drives — larger drives are truncated to match the smallest. Synology SHR allows mixed drive sizes and optimizes capacity automatically. This is SHR’s main advantage over traditional RAID.
RAID rebuild time depends on drive size: 4TB ≈ 8-12 hours, 8TB ≈ 16-24 hours, 12TB ≈ 24-36 hours, 16TB+ ≈ 36-48+ hours. During rebuild, the array is vulnerable. This is why RAID 6/SHR-2 is recommended for large drives — it survives a second failure during rebuild.
No, RAID is NOT a backup. RAID protects against drive failure only. It does NOT protect against: accidental deletion, ransomware/viruses, fire or theft, controller failure, or file corruption. Always maintain separate backups regardless of RAID level.
RAID 10 combines RAID 1 (mirroring) and RAID 0 (striping). Data is first mirrored across drive pairs, then striped across pairs for performance. RAID 10 offers excellent speed and can survive 1 drive failure per mirror pair. Capacity is 50% of total drives. Requires minimum 4 drives (even number).
Related Resources
- SHR vs RAID Explained — Deep dive into Synology Hybrid RAID
- Synology RAID Setup Guide — Step-by-step configuration
- Synology Compatible Drives — Full drive database
- Best Synology NAS 2026 — NAS buying guide
- DS925+ vs DS923+ Comparison — 4-bay NAS comparison
Last Updated: February 2026 | RAID Calculator v1.0