Calculate usable RAID capacity, parity overhead, and fault tolerance for RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10 arrays. Estimate storage efficiency and redundancy for NAS, server, and CCTV NVR deployments.
Overview
The RAID Calculator estimates usable capacity, parity overhead, redundancy, and fault tolerance for RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10 arrays. It helps system administrators, NAS owners, server builders, and CCTV NVR planners choose the right RAID level and drive count for their storage and reliability needs.
Common Use Cases
NAS capacity planning
Server storage design
CCTV NVR storage planning
RAID level selection
Drive replacement budgeting
Data redundancy planning
Storage upgrade planning
Homelab storage builds
Backup server sizing
Storage efficiency analysis
How to Use
1
Select the RAID level you want to evaluate.
2
Enter the total number of drives in the array.
3
Enter the size of a single drive in terabytes.
4
Optionally enter how many hot spare drives are reserved.
5
Review raw capacity, usable capacity, capacity overhead, redundancy factor, and fault tolerance.
Example Scenario
Four-Drive NAS with RAID 5
A small office builds a 4-bay NAS using four 4 TB drives. With RAID 5 the usable capacity is 12 TB (one drive of parity), and the array tolerates a single drive failure without data loss.
Technical Notes
RAID 0 stripes data across all drives with no parity. It offers maximum capacity and performance but provides zero redundancy, so any single drive failure loses the whole array.
RAID 1 mirrors data across all drives. Usable capacity equals the size of a single drive, and all but one drive can fail without losing data.
RAID 5 stripes data with distributed parity across the array. It loses one drive of capacity to parity and tolerates a single drive failure.
RAID 6 uses two parity blocks across the array. It loses two drives of capacity and tolerates two simultaneous drive failures.
RAID 10 mirrors pairs of drives and stripes across the pairs. It combines speed with redundancy but uses half the raw capacity, and each mirror pair tolerates one failure.
A hot spare is a standby drive that automatically replaces a failed drive in the array. It is reserved for replacement and does not add usable capacity.
Capacity overhead is the portion of raw capacity consumed by parity or mirroring. Lower overhead means more usable storage but usually less redundancy.
Fault tolerance indicates how many drives can fail at the same time before data loss occurs.
Common Mistakes
Choosing RAID 0 for critical data
Using RAID 5 with very large drives and no hot spare
Assuming RAID 1 doubles usable capacity
Using an odd number of drives for RAID 10
Ignoring rebuild time after a drive failure
Mixing different drive sizes in the array
Forgetting to reserve hot spares in the drive count
Frequently Asked Questions
RAID 0 for speed with no redundancy, RAID 1 for mirrored safety, RAID 5 as a balanced choice for 3 or more drives, RAID 6 for stronger protection with 4 or more drives, and RAID 10 when performance and redundancy both matter.
RAID 5 provides N minus 1 drives of usable capacity, where N is the number of drives. For example, four 4 TB drives give 12 TB usable.
Many RAID controllers limit the array to the size of the smallest drive. Matching drive sizes is recommended to avoid wasted capacity.
A hot spare is a drive that stays idle in the system and automatically replaces a failed drive, helping the array rebuild itself without waiting for a human to swap hardware.
RAID protects against drive failure, not against deletion, corruption, theft, or disasters. Always keep an independent backup in addition to RAID.