RAID Calculator: Usable Capacity, Fault Tolerance and Speed

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The RAID configuration determines how drives are combined for speed and redundancy.
Total number of physical drives in the array (per RAID group for RAID 50/60).
Capacity of each individual drive.
Hard drive manufacturers use SI units (1 TB = 1000 GB). Operating systems often report binary units (1 TiB = 1024 GiB).
Leave at 0 to skip cost calculations.
USD
Usable storageStandard redundancy
12.00 TB

Total storage available for your data after RAID overhead

Raw capacity16.00 TB
Storage efficiency0.8%
Drives you can lose1
Read speed gain3x faster
Write speed gain~25% (write penalty)
Total drives4
Storage efficiency0.8%
Fault tolerance (drives)1

12.00 TB usable with RAID 5 using 4 drives

  • Distributed parity - one drive equivalent of parity spread across all drives.
  • Storage efficiency is 75.0% - Good balance of capacity, speed, and redundancy.
  • One drive can fail and the array will continue operating during rebuild.
  • Weakness: Slow writes due to parity calculation; risky during rebuild on large drives.

Next stepRAID is not a backup. Always keep at least one off-site or cloud backup of critical data regardless of your RAID level.

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