RAID Calculator

Calculate RAID configurations with mixed disk sizes. Plan optimal storage arrays for NAS, servers, and enterprise systems.

New Feature: Now supports mixed disk sizes! In traditional RAID, all disks will be limited to the smallest disk's capacity. Some modern RAID implementations (like ZFS RAID-Z) can utilize full capacity of each disk.

Select the RAID level for your storage array
Total physical disks in the array
Capacity of each individual disk (all disks same size)
In traditional RAID, all disks will be limited to the smallest disk's capacity. Each disk's effective capacity is shown below.
Disk Capacity Summary
Smallest Disk: 4 TB
Largest Disk: 4 TB
Average Disk: 4 TB
Total Raw Capacity: 16 TB
Type of storage drives used
RAID implementation type affects capacity calculation
NAS Upgrade (Mixed: 2x4TB + 2x8TB RAID 5)
Budget Array (Mixed: 3x2TB + 3x4TB RAID 6)
Hybrid Storage (2x1TB SSD + 4x4TB HDD RAID 10)
ZFS Pool (Mixed: 4x6TB + 2x10TB RAID-Z2)
RAID Array Visualization
Data Disk
Parity Disk
Mirror Disk
Failed Disk

Understanding RAID with Mixed Disk Sizes

RAID (Redundant Array of Independent Disks) is a data storage virtualization technology that combines multiple physical disk drives into one or more logical units. With mixed disk sizes, capacity calculation becomes more complex.

How Traditional RAID Handles Mixed Disk Sizes:

  • Smallest Disk Limitation: Traditional RAID (0, 1, 5, 6, 10) limits all disks to the smallest disk's capacity
  • Capacity Waste: Larger disks have unused space that cannot be utilized
  • Modern Solutions: ZFS RAID-Z, Unraid, and Windows Storage Spaces offer better mixed-size support
  • Planning Consideration: Always calculate effective capacity before purchasing disks

Example Calculation for Mixed Disk RAID 5:

For a RAID 5 array with disks: 2TB, 4TB, 4TB, 6TB

  • Smallest disk: 2TB
  • Each disk's effective capacity: 2TB
  • Total raw capacity: 8TB (4 × 2TB)
  • Usable capacity: 6TB (3 × 2TB, RAID 5 overhead)
  • Wasted capacity: 8TB (4TB - 2TB = 2TB wasted on each larger disk)

RAID Level Comparison for Mixed Disks

RAID Level Min Disks Mixed Size Support Capacity Efficiency Fault Tolerance Best Use Case
RAID 0 2 Limited by smallest disk 100% of smallest disk × count None Non-critical performance
RAID 1 2 Limited by smallest disk Size of smallest disk n-1 disks Critical data, small arrays
RAID 5 3 Limited by smallest disk (n-1) × smallest disk 1 disk Balanced performance & redundancy
RAID 6 4 Limited by smallest disk (n-2) × smallest disk 2 disks Large arrays, critical data
RAID 10 4 Limited by smallest disk (n/2) × smallest disk 1 disk per mirror High performance databases
ZFS RAID-Z1 3 Better utilization Sum - largest disk 1 disk Mixed sizes, ZFS filesystem
ZFS RAID-Z2 4 Better utilization Sum - 2 largest disks 2 disks Large mixed arrays

Best Practices for Mixed Disk Arrays

1

Calculate Waste First: Use this calculator to estimate wasted capacity before purchasing disks. Larger disks will have unused space in traditional RAID.

2

Consider Modern Solutions: ZFS RAID-Z or Unraid may be better options for arrays with mixed disk sizes as they can utilize more of each disk's capacity.

3

Group Similar Sizes: When possible, use disks of similar sizes in the same RAID group to minimize wasted capacity.

4

Plan for Future Expansion: Consider buying larger disks than currently needed, as adding larger disks later may require replacing multiple disks to increase capacity.

Important Consideration:

When mixing disk sizes in traditional RAID, the larger disks will have unused capacity. This wasted space cannot be recovered without replacing the smaller disks or rebuilding the entire array with different disk sizes. Always verify compatibility with your RAID controller or software implementation.

Frequently Asked Questions

In traditional RAID implementations (RAID 0, 1, 5, 6, 10), when disks of different sizes are used, the entire array is limited to the capacity of the smallest disk. Each larger disk will have unused space that cannot be utilized by the RAID array. This is because RAID stripes or mirrors data evenly across all disks.

With traditional RAID, adding a larger disk to an existing array typically won't increase capacity unless you replace all disks with larger ones or use a specific expansion feature. Some RAID implementations allow online expansion, but the new disk's capacity may be limited to the smallest disk in the array. With ZFS or Unraid, you have more flexibility to add larger disks.

For arrays with mixed disk sizes, ZFS RAID-Z or Unraid are often better choices than traditional RAID. ZFS RAID-Z can utilize more of each disk's capacity, while Unraid is specifically designed for mixed disk environments. Traditional RAID should only be used with mixed sizes if you understand and accept the capacity limitations.

The wasted capacity depends on the size difference between disks. For example, if you have one 2TB disk and three 4TB disks in a RAID 5 array, each 4TB disk will only use 2TB, wasting 2TB per disk (6TB total wasted). This calculator shows you exactly how much capacity will be wasted before you build your array.

Software RAID (like ZFS, mdadm, or Windows Storage Spaces) generally offers better support for mixed disk sizes than hardware RAID controllers. Many hardware RAID controllers require identical disks or limit arrays to the smallest disk's capacity. Software solutions also offer more flexibility for future expansion and mixed-size configurations.