Raid Capacity Calculator

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RAID Capacity Calculator

Minimum drives for RAID 5: 3
Hot spares don't add capacity but improve reliability

Choosing the right RAID configuration is critical when designing storage systems for servers, NAS devices, and enterprise infrastructure. While RAID improves performance, fault tolerance, or both, it also reduces usable storage due to redundancy and overhead. The RAID Capacity Calculator helps you accurately determine usable capacity, storage efficiency, and fault tolerance for different RAID levels.

This calculator eliminates confusion by instantly computing how much space is available after redundancy, hot spares, and file system overhead. Whether you’re an IT professional, system administrator, or home lab enthusiast, this tool allows you to plan storage with confidence.

What Is RAID?

RAID (Redundant Array of Independent Disks) combines multiple physical drives into a single logical unit to improve performance, reliability, or both. Different RAID levels balance these factors differently:

  • Some RAID levels maximize performance
  • Others prioritize data protection
  • Some offer a balanced approach

Understanding usable capacity is essential before deploying RAID in production environments.

What This RAID Capacity Calculator Does

This calculator provides a complete overview of your RAID configuration, including:

  • Total raw storage capacity
  • Usable capacity after RAID redundancy
  • Capacity lost to parity or mirroring
  • Storage efficiency percentage
  • Fault tolerance (number of drive failures supported)
  • Impact of hot spare drives
  • File system overhead adjustment
  • Performance and use-case recommendations

All calculations are performed instantly, helping you compare RAID levels side by side.

RAID Levels Supported

RAID 0 – Striping (No Redundancy)

  • Combines all drives into one large volume
  • Maximum performance and capacity
  • No fault tolerance
  • Best for temporary or non-critical data

RAID 1 – Mirroring

  • Data is duplicated across drives
  • Excellent redundancy
  • Usable capacity is 50% of raw storage
  • Ideal for critical data and OS drives

RAID 5 – Striping with Parity

  • Requires at least 3 drives
  • Can survive one drive failure
  • Good balance of capacity and protection
  • Common in file servers and NAS systems

RAID 6 – Dual Parity

  • Requires at least 4 drives
  • Can survive two drive failures
  • Higher redundancy than RAID 5
  • Suitable for large arrays

RAID 10 – Mirrored Stripe

  • Combines RAID 1 and RAID 0
  • High performance and strong redundancy
  • Requires even number of drives
  • Popular for databases and virtualization

RAID 50 – Striped RAID 5

  • RAID 5 arrays striped together
  • Improved performance and redundancy
  • Ideal for enterprise environments

RAID 60 – Striped RAID 6

  • RAID 6 arrays striped together
  • Very high fault tolerance
  • Used in mission-critical systems

JBOD – Just a Bunch of Disks

  • No RAID logic
  • Full usable capacity
  • No redundancy
  • Simple disk aggregation

How to Use the RAID Capacity Calculator

Step 1: Select RAID Level

Choose the RAID configuration that best fits your needs.

Step 2: Enter Number of Drives

Specify how many disks are in your array. Minimum requirements are automatically enforced for each RAID level.

Step 3: Enter Drive Size

Input the capacity of each drive and select the appropriate unit (GB, TB, or PB).

Step 4: Choose Unit Type

  • Decimal (1 TB = 1,000 GB)
  • Binary (1 TiB = 1,024 GiB)

This distinction is important for accurate calculations.

Step 5: Add Hot Spare Drives (Optional)

Hot spares improve reliability but do not add usable storage.

Step 6: Apply File System Overhead

Enter a percentage to account for formatting, metadata, and system usage.

Step 7: Click Calculate

Instantly view all RAID capacity details and recommendations.

Example RAID Capacity Calculations

Example 1: RAID 5 Configuration

  • 4 drives
  • 4 TB per drive
  • No hot spare

Results:

  • Total Raw Capacity: 16 TB
  • Usable Capacity: 12 TB
  • Lost to Redundancy: 4 TB
  • Storage Efficiency: 75%
  • Fault Tolerance: 1 drive failure

Example 2: RAID 10 Configuration

  • 6 drives
  • 2 TB per drive

Results:

  • Total Raw Capacity: 12 TB
  • Usable Capacity: 6 TB
  • Lost to Redundancy: 6 TB
  • Storage Efficiency: 50%
  • Fault Tolerance: Multiple drives (one per mirror)

Example 3: RAID 6 with File System Overhead

  • 8 drives
  • 10 TB per drive
  • 5% file system overhead

Results:

  • Total Raw Capacity: 80 TB
  • Usable Capacity: 60 TB
  • After Overhead: 57 TB
  • Fault Tolerance: 2 drives

Understanding Storage Efficiency

Storage efficiency shows how much of your raw storage is usable:Efficiency=Usable CapacityTotal Raw Capacity×100\text{Efficiency} = \frac{\text{Usable Capacity}}{\text{Total Raw Capacity}} \times 100Efficiency=Total Raw CapacityUsable Capacity​×100

Higher efficiency means less space lost to redundancy—but often at the cost of fault tolerance.

Why Use This RAID Capacity Calculator?

Key Benefits

  • ✅ Prevents under- or over-provisioning
  • ✅ Compares RAID levels accurately
  • ✅ Accounts for real-world overhead
  • ✅ Improves storage planning decisions
  • ✅ Ideal for NAS, servers, and data centers
  • ✅ Beginner-friendly yet enterprise-ready

This calculator helps you choose the right RAID setup before investing in hardware.

Performance & Use-Case Insights

  • RAID 0: High-speed workloads, no data protection
  • RAID 1: System drives, critical files
  • RAID 5: General storage and file servers
  • RAID 6: Large arrays with high reliability needs
  • RAID 10: Databases, virtualization, heavy I/O
  • RAID 50/60: Enterprise-level performance and redundancy

15 Frequently Asked Questions (FAQs)

  1. What is usable RAID capacity?
    The storage available after redundancy and overhead.
  2. Does RAID increase storage size?
    No, RAID improves performance and reliability, not raw capacity.
  3. What RAID level is most efficient?
    RAID 0 and JBOD offer the highest efficiency but no protection.
  4. Which RAID is safest?
    RAID 6 and RAID 60 provide high fault tolerance.
  5. Do hot spares increase capacity?
    No, they only improve reliability.
  6. Why is RAID 10 only 50% efficient?
    Because data is mirrored.
  7. What is file system overhead?
    Space used for formatting, metadata, and system files.
  8. Is RAID a backup?
    No, RAID is not a replacement for backups.
  9. What unit type should I choose?
    Binary units are more accurate for operating systems.
  10. Can RAID survive multiple drive failures?
    Yes, depending on the RAID level.
  11. Is JBOD safe?
    JBOD offers no redundancy.
  12. Which RAID is best for NAS?
    RAID 5 or RAID 6 are common choices.
  13. Does drive size affect RAID capacity?
    Yes, all drives are limited by the smallest disk.
  14. Can I mix drive sizes?
    Yes, but capacity is based on the smallest drive.
  15. Is this calculator suitable for enterprise use?
    Yes, it supports advanced RAID configurations.

Conclusion

The RAID Capacity Calculator is an essential tool for accurate storage planning. By accounting for RAID level, disk count, redundancy, hot spares, and file system overhead, it provides a realistic view of usable capacity and reliability. Whether you’re building a home NAS or designing enterprise infrastructure, this calculator ensures smarter, safer storage decisions.

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