RAID Storage Calculator
RAID (Redundant Array of Independent Disks) combines multiple drives to provide fault tolerance, increased performance, or expanded capacity. Each RAID level makes a different trade-off between usable storage and the number of drive failures the array can survive. This calculator computes usable capacity, redundancy overhead, fault tolerance (number of drives that can fail without data loss), and the storage efficiency percentage for RAID levels 0, 1, 5, 6, and 10. Enter the number of drives and drive size to compare options and choose the right RAID level for your workload.
RAID usable capacity formulas
RAID 0: usable = N * drive_size (efficiency = 100%)
RAID 1: usable = drive_size (efficiency = 1/N * 100%)
RAID 5: usable = (N-1) * drive_size (efficiency = (N-1)/N * 100%)
RAID 6: usable = (N-2) * drive_size (efficiency = (N-2)/N * 100%)
RAID 10: usable = (N/2) * drive_size (efficiency = 50%)
RAID level comparison
- RAID 0: Maximum performance and capacity, zero fault tolerance. Use only for scratch storage where data loss is acceptable.
- RAID 1: Maximum redundancy for small arrays (2-4 drives). Good for OS and boot drives.
- RAID 5: Good balance of capacity, performance, and redundancy for 3-6 drives. Most common for NAS devices.
- RAID 6: Better protection for larger arrays. Tolerates 2 simultaneous failures - important as drive sizes and rebuild times increase.
- RAID 10: Best performance for transactional workloads (databases). More expensive but faster rebuild than RAID 5/6.
Frequently asked questions
What is RAID and what levels are most common?
RAID (Redundant Array of Independent Disks) combines multiple drives to improve performance, capacity, or fault tolerance. RAID 0 stripes data across drives for performance with no redundancy. RAID 1 mirrors data for full redundancy. RAID 5 stripes data with a parity block (tolerates 1 drive failure). RAID 6 uses two parity blocks (tolerates 2 drive failures). RAID 10 (1+0) mirrors then stripes for both performance and redundancy.
How much usable capacity does each RAID level provide?
RAID 0: 100% of raw capacity (no redundancy). RAID 1: 50% of raw capacity (mirroring). RAID 5: (N-1)/N of raw capacity, where N is drive count. RAID 6: (N-2)/N of raw capacity. RAID 10: 50% of raw capacity (requires even number of drives, minimum 4).
What is the difference between RAID and backup?
RAID provides availability against drive failures but is not a backup. RAID does not protect against accidental deletion, file corruption, ransomware, or controller failures. Backups create separate copies of data at a point in time. Both RAID and backup are necessary components of a complete data protection strategy.
What drive count is optimal for RAID 5?
RAID 5 works with a minimum of 3 drives. Common configurations are 4, 5, 6, or 8 drives. Beyond 6-7 drives, rebuild time after a single drive failure increases to the point where a second drive failure during rebuild becomes statistically likely. For large arrays, RAID 6 or erasure coding is recommended.
What is the RAID 5 write hole problem?
The RAID 5 write hole is a data consistency vulnerability where a power failure during a write can leave parity data inconsistent with the data blocks. This can lead to silent data corruption. Modern RAID controllers use write-back cache with battery backup, write-ahead logging, or ZFS-style copy-on-write to avoid this problem.
Official sources
- NIST: SP 800-111 - Guide to Storage Encryption Technologies.
- IEEE: IEEE Computer Society - RAID: A Case for Redundant Arrays.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.