Developer Tools

RAID
Calculator

Add your drives, pick a RAID level, and get usable capacity, fault tolerance and a full space breakdown instantly — including mixed drive sizes and SHR/SHR-2.

9 RAID types

Mixed drive sizes

Instant results

# 4x 4TB, RAID 5
raw 16 TB
usable 12 TB
parity 1 drive
tolerance 1 failure

Drives

RAID Type

Advanced Options

Hot Spares

Reserved from the last drives in the list — standby until a failure.

Filesystem

Reserve ~10GB per drive for system space

Raw Capacity

—

Usable Capacity

—

Efficiency

—

Protection

—

RAID Type Reference

Type	Min Drives	Usable Capacity	Fault Tolerance
Basic	1	Sum of all drives	None
JBOD	2	Sum of all drives	None
RAID 0	2	N × smallest drive	None
RAID 1	2	1 × smallest drive	N − 1 drives
RAID 5	3	(N − 1) × smallest drive	1 drive
RAID 6	4	(N − 2) × smallest drive	2 drives
RAID 10	4 (even)	(N ÷ 2) × smallest drive	Up to N ÷ 2 drives
SHR	3	Tiered — RAID 5-equivalent, mixed sizes	1 drive
SHR-2	4	Tiered — RAID 6-equivalent, mixed sizes	2 drives

Frequently Asked Questions

What is SHR and how is it different from RAID 5?

Synology Hybrid RAID (SHR) gives the same single-drive fault tolerance as RAID 5, but it works in size-based tiers so mismatched drive sizes waste far less space than plain RAID 5, which caps every drive at the size of the smallest one.

Why is my usable capacity smaller than the sum of my drives?

Redundant RAID levels dedicate part of the raw capacity to parity or mirror copies, filesystems reserve a small percentage for metadata, and drives larger than the smallest one in the array can have unused space in levels that require equal-size members.

Should I use RAID 5 or RAID 6?

RAID 6 survives two simultaneous drive failures instead of one, which matters more as arrays get bigger and rebuild times get longer. The tradeoff is a second drive's worth of capacity spent on parity.

What is a hot spare?

A hot spare is a drive kept idle in the array. If a member drive fails, the array automatically rebuilds onto the spare, restoring redundancy without you needing to physically swap a disk.

Does RAID replace backups?

No. RAID protects against drive failure, not against accidental deletion, ransomware, or the whole enclosure being lost. Keep a separate backup regardless of RAID level.

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