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RAID Capacity Planner

Build your drive array. See where the space goes—and what redundancy protects.

Focus on this tool.

Build your drive array

4 installed · 0 spares

Give each bay its own capacity. Compare layouts without rebuilding your drive list.

Bay 1

Bay 1 capacity (TB)

Hot spare

4 TB in array · 0 TB unused

Bay 2

Bay 2 capacity (TB)

Hot spare

4 TB in array · 0 TB unused

Bay 3

Bay 3 capacity (TB)

Hot spare

4 TB in array · 0 TB unused

Bay 4

Bay 4 capacity (TB)

Hot spare

4 TB in array · 0 TB unused

Add a drive

Uniform array & example layouts

Drive count

Each drive (TB)

These actions replace the current drive list and clear simulated failures.

RAID 5 capacity

Planning estimate

12 TB available of 16 TB installed

Available data: 12 TB75%
Planning reserve: 0 TB0%
Redundancy: 4 TB25%
Unused size: 0 TB0%
Hot spares: 0 TB0%

Protection: Any 1 active drive failure.

(N − 1) × smallest active drive (4 TB).

Planning reserve / overhead (%)Optional fraction of post-RAID usable space. 0% means before formatting; not a vendor-specific overhead calculation.

Drive labels stay in decimal TB. 1 TB = 10¹² bytes; 1 TiB = 2⁴⁰ bytes.

What if a drive fails?

Simulation only · no hardware access

Toggle bays to simulate simultaneous failures in an initially healthy array, before any rebuild. The capacity estimate above stays unchanged.

No active-drive failures. 0 active drives and 0 spares marked failed. This is a redundancy model, not a guarantee of successful recovery. Hot spares do not increase failure tolerance before a rebuild completes.

Same drives. Different tradeoffs.

Available data / installed capacity

Every card uses your exact drive list, spares, and planning reserve. Bars use the same colors as the capacity chart.

RAID 0

16 TB

100% available · 0 TB unused
No drive-failure protection.

RAID 1

4 TB

25% available · 0 TB unused
Any 3 active drive failures.

RAID 5

Selected

12 TB

75% available · 0 TB unused
Any 1 active drive failure.

RAID 6

8 TB

50% available · 0 TB unused
Any 2 active drive failures.

RAID 10

8 TB

50% available · 0 TB unused
One failure in each mirror pair; never both members of a pair.

SHR-1

Estimate

12 TB

75% available · 0 TB unused
Any 1 active drive failure.

SHR-2

Estimate

8 TB

50% available · 0 TB unused
Any 2 active drive failures.

JBOD

16 TB

100% available · 0 TB unused
No drive-failure protection.

How this model works & source references

Traditional RAID 0, 1, 5, 6 and 10 use the smallest active drive in this model. RAID 1 is one mirror across all active drives. RAID 10 pairs consecutive active bays and uses a common smallest-drive stripe size. JBOD sums active capacities without protection. The per-bay colors show capacity accounting, not actual stripe locations; parity is distributed in real RAID 5/6 arrays.

SHR-1 and SHR-2 are locally implemented, idealized new-pool estimates inspired by Synology’s documented capacity-tier approach. SHR-1 uses redundant tiers with at least two drives; SHR-2 requires at least four per tier and reserves two drive-equivalents. Extra capacity without enough matching members stays unused. Single-drive SHR has no protection. These estimates do not validate DSM support, drive compatibility, expansion history, system partitions, or vendor-specific limits.

Planning reserve is deducted from post-RAID usable capacity, not from raw drive capacity. Formatting, filesystem metadata, snapshots, and vendor system partitions may differ. Read/write speed and rebuild time depend on hardware and workload and are not promised here. RAID is not a backup.

Sources: Synology RAID calculator, Synology’s SHR explanation, QNAP’s RAID types, and ReclaiMe’s RAID calculator. This independent tool is not endorsed by those vendors.

Calculated in your browser. Inputs and files aren’t uploaded or saved. Tool sources & licenses