RAID Calculator
Calculate usable storage capacity and fault tolerance for any RAID configuration. Supports RAID 0, 1, 5, 6, 10, 50, 60, JBOD, and Synology SHR with file system overhead.
Distributes parity across all drives. Survives one drive failure. Good balance of capacity and protection.
Usable Capacity
11.82 TB
75.0% storage efficiency
RAID level comparison
| Level | Min | Fault tolerance | Capacity formula |
|---|---|---|---|
| RAID 0 | 2 | None | N × Size |
| RAID 1 | 2 | N−1 drives | 1 × Size |
| RAID 5 | 3 | 1 drive | (N−1) × Size |
| RAID 6 | 4 | 2 drives | (N−2) × Size |
| RAID 10 | 4 | 1/mirror pair | (N÷2) × Size |
| RAID 50 | 6 | 1/sub-array | (N−2) × Size* |
| RAID 60 | 8 | 2/sub-array | (N−4) × Size* |
| JBOD | 1 | None | N × Size |
| SHR | 1 | 1 drive (SHR-1) | ≈(N−1) × Size |
* Assumes 2 sub-arrays. N = number of drives.
How RAID capacity is calculated
Each RAID level has a different formula for usable capacity based on how data, parity, and mirroring are distributed:
RAID 0: N × drive_size (no redundancy)
RAID 1: 1 × drive_size (full mirror)
RAID 5: (N − 1) × drive_size
RAID 6: (N − 2) × drive_size
RAID 10: (N ÷ 2) × drive_size
After calculating the RAID capacity, we subtract file system overhead (if selected) to give you the actual usable capacity you can store data on.
Choosing the right RAID level
Maximum speed
RAID 0 stripes data for top read/write performance, but any drive failure means total data loss.
Simple redundancy
RAID 1 mirrors two drives for easy recovery, but you lose 50% of total capacity.
Balanced protection
RAID 5 offers a good balance of capacity, performance, and single-drive fault tolerance.
Extra safety
RAID 6 handles two simultaneous drive failures — essential for 5+ drive arrays with long rebuild times.
Performance + safety
RAID 10 combines mirroring and striping for the best of both worlds, at 50% capacity cost.
Mixed drives (NAS)
Synology SHR optimizes capacity when you have different-sized drives in a NAS.
Frequently asked questions
What is RAID?
RAID (Redundant Array of Independent Disks) is a technology that combines multiple physical drives into a single logical unit for improved performance, redundancy, or both. Different RAID levels offer different trade-offs between capacity, speed, and fault tolerance.
Which RAID level should I use?
For home NAS: RAID 5 or SHR (if using Synology). For critical data with budget: RAID 6 or RAID 10. For maximum performance without redundancy: RAID 0. For simple mirroring: RAID 1. For enterprise: RAID 6, RAID 50, or RAID 60 depending on drive count.
Why does RAID 10 require an even number of drives?
RAID 10 creates mirrored pairs first, then stripes across those pairs. Each pair needs exactly 2 drives. With an odd number (e.g., 5), one drive would be unpaired and the array cannot be built. Use RAID 5 instead if you have an odd number of drives.
What is the difference between RAID 5 and RAID 6?
RAID 5 uses single parity (one drive's worth of redundancy) and can survive one drive failure. RAID 6 uses double parity (two drives' worth) and can survive two simultaneous failures. RAID 6 is recommended for arrays with 5+ drives where rebuild times are long.
What is Synology Hybrid RAID (SHR)?
SHR is Synology's proprietary RAID system that optimizes capacity when using mixed drive sizes. It partitions larger drives into chunks matching smaller drives, creating RAID 5-like redundancy. With identical drives, SHR capacity equals RAID 5. SHR-2 provides double redundancy like RAID 6.
What is file system overhead?
File systems (ext4, NTFS, ZFS, etc.) reserve space for metadata, journals, and internal structures. This reduces usable capacity by 0.5%–2% depending on the file system. Our calculator includes this overhead for accurate estimates.
Is RAID a backup?
No! RAID protects against drive failure but NOT against accidental deletion, ransomware, fire, theft, or controller failure. Always maintain separate backups following the 3-2-1 rule: 3 copies, 2 different media, 1 offsite.
Why is my actual usable capacity less than calculated?
Drive manufacturers use decimal gigabytes (1 GB = 1,000,000,000 bytes) while operating systems use binary gibibytes (1 GiB = 1,073,741,824 bytes). A "4 TB" drive is actually about 3.64 TiB. Our calculator uses the manufacturer's advertised capacity.
What is JBOD?
JBOD (Just a Bunch Of Disks) concatenates drives into a single volume without any striping or redundancy. If one drive fails, you only lose data on that specific drive. It gives you the total capacity of all drives combined.
Can I mix drive sizes in a RAID array?
In traditional RAID (0, 1, 5, 6, 10), all drives are treated as the size of the smallest drive. Larger drives waste capacity. SHR (Synology) and some ZFS configurations can optimize mixed sizes. This calculator assumes identical drives for traditional RAID levels.