Which RAID level is best for a home NAS?

RAID 5 or RAID 6 are common choices. RAID 5 offers good capacity efficiency with single-disk fault tolerance. RAID 6 is safer for large-drive arrays because it tolerates two simultaneous failures. For two-drive setups, RAID 1 (mirror) is the standard choice.

Can I mix different sized drives in a RAID array?

Traditional RAID uses the capacity of the smallest drive for all members. A 4 TB and an 8 TB drive in RAID 1 yields only 4 TB usable. Some modern NAS systems (SHR, Unraid) can use mixed sizes more efficiently.

How long does a RAID rebuild take?

Rebuild times depend on drive size and array activity. A 4 TB drive in a busy RAID 5 array can take 12–24 hours or more to rebuild. During this time, the array is vulnerable to a second failure, which is why RAID 6 is recommended for large drives.

What is RAID 10 vs. RAID 01?

RAID 10 mirrors pairs of drives, then stripes across the pairs. RAID 01 stripes first, then mirrors the stripes. RAID 10 is preferred because it can tolerate more specific failure combinations and rebuilds faster.

Is RAID 0 ever appropriate?

RAID 0 is suitable only for non-critical data where maximum speed and capacity are needed—such as video editing scratch disks or temporary render farms. Any single drive failure destroys all data in the array.

A hot spare is an unused drive that automatically replaces a failed drive, starting the rebuild process immediately. This reduces the vulnerability window from hours (waiting for a replacement) to minutes. Most enterprise arrays include at least one hot spare.

RAID Calculator

Calculate usable capacity, fault tolerance, and minimum disk requirements for RAID 0, 1, 5, 6, and 10 configurations.

Number of Disks

Disk Size

RAID Level

Hot Spares

Raw Capacity

20.00 TB

5 active drive(s)

Usable Capacity

16.00 TB

80.0% efficiency

Parity/Overhead

4.00 TB

20.0% of raw

Fault Tolerance

1 disk(s)

can tolerate 1 failure(s)

Hot Spares: 1 spare drive(s) ready for auto-replacement. Rebuild starts immediately on failure.

RAID Level Comparison (with 6 disks @ 4 TB)

Level	Usable	Efficiency	Fault Tol.	Est. Rebuild
RAID 2	24.00 TB	100.0%	0 disk(s)	0.5h
RAID 2	4.00 TB	16.7%	5 disk(s)	0.5h
RAID 3	20.00 TB	83.3%	1 disk(s)	0.5h
RAID 4	16.00 TB	66.7%	2 disk(s)	0.5h
RAID 4	12.00 TB	50.0%	1 disk(s)	0.5h

Note: Estimated rebuild time assumes ~100 MB/s throughput. Large modern drives take 12–48+ hours. RAID 5 with 8 TB+ drives is risky; consider RAID 6 or RAID 10 for production.

Planning notes, formulas, and examples

About the RAID Calculator

RAID (Redundant Array of Independent Disks) combines multiple physical drives into a single logical volume with varying levels of performance and fault tolerance. Choosing the right RAID level is one of the most impactful storage decisions an IT team makes. RAID 0 maximizes capacity and speed but offers zero protection—one dead disk means total data loss. RAID 1 mirrors drives for excellent redundancy but uses only half the raw capacity. RAID 5 and 6 use parity to balance capacity with fault tolerance, while RAID 10 combines mirroring and striping for top performance and redundancy.

This calculator shows the usable capacity, fault tolerance (how many drives can fail), and minimum disk count for each RAID level. Enter the number and size of your drives, select a RAID level, and review the resulting capacity and fault-tolerance tradeoffs. It's essential for anyone building or planning a storage array—from home NAS setups to enterprise SAN deployments.

When This Page Helps

Choosing the wrong RAID level can waste expensive storage or leave you unprotected against drive failures. This calculator shows the trade-offs between capacity, performance, and fault tolerance for each RAID level, helping you make an informed decision.

How to Use the Inputs

Enter the number of disks in your array.
Enter the capacity of each disk in TB or GB.
Select the desired RAID level.
Review usable capacity, fault tolerance, and efficiency.
Compare different RAID levels to find the best trade-off.
Factor the results into your storage procurement plan.

Formula used

RAID 0: usable = disks × size; RAID 1: usable = size (mirror); RAID 5: usable = (disks − 1) × size; RAID 6: usable = (disks − 2) × size; RAID 10: usable = (disks / 2) × size

Example Calculation

Result: 20 TB usable

With 6 disks of 4 TB each, RAID 5 uses one disk's worth for parity: (6 − 1) × 4 = 20 TB usable out of 24 TB raw. The array can tolerate exactly 1 disk failure. Storage efficiency is 83.3%.

Tips & Best Practices

RAID is not a backup—always maintain separate backups regardless of RAID level.
RAID 5 with very large drives is risky: rebuild times are long and a second failure during rebuild means total loss.
RAID 6 is recommended for arrays with drives larger than 2 TB due to the high rebuild risk of RAID 5.
RAID 10 is preferred for write-heavy workloads like databases due to superior write performance.
Use hot spares to reduce the window of vulnerability during rebuilds.
All drives in a RAID array should be the same size; the array uses the smallest drive's capacity.

RAID Level Comparison

RAID 0 delivers maximum capacity and sequential throughput but zero fault tolerance. RAID 1 provides perfect redundancy at 50% capacity efficiency. RAID 5 uses distributed parity for single-fault tolerance at good efficiency. RAID 6 adds a second parity disk for dual-fault tolerance—essential for large arrays. RAID 10 combines mirroring and striping for the best mix of performance and resilience.

When to Use Each Level

Use RAID 1 for OS boot drives and small critical volumes. RAID 5 works well for read-heavy file servers with moderate capacity needs. RAID 6 is the standard for general-purpose storage with large drives. RAID 10 is the choice for databases and write-intensive applications where performance and redundancy both matter.

Beyond Traditional RAID

Modern solutions like ZFS RAIDZ, Ceph, and erasure coding offer more flexible alternatives with better scalability and efficiency than traditional hardware RAID. Consider these for new deployments, especially at scale.

Sources & Methodology

Last updated: February 8, 2026

Frequently Asked Questions

RAID 5 or RAID 6 are common choices. RAID 5 offers good capacity efficiency with single-disk fault tolerance. RAID 6 is safer for large-drive arrays because it tolerates two simultaneous failures. For two-drive setups, RAID 1 (mirror) is the standard choice.