Choose your drives

Add each physical drive once. Results update as soon as the selection changes.

Up to 24 drives · 1 PB per drive

HDD sizes

SSD sizes

Custom drive

Capacity

Unit

Drive type

Enter a positive capacity up to 1 PB. Decimal units use base 10; GiB and TiB use base 2.

Selected drives

No drives selected.

Drive count: 0
Raw capacity: 0 GB

Choose a preset above or add a custom drive.

Layout comparison

All supported layouts stay visible. Layouts that need more or different drives explain why they are unavailable.

Add drives to compare layouts

Capacity results appear as soon as at least one drive is selected.

What this tool does

This calculator compares the RAID-level capacity available from a chosen set of drives across common RAID, ZFS and selected Synology layouts.

It reports raw capacity, usable capacity, protection capacity, unused space, efficiency and drive-failure tolerance without recommending one layout as best for every workload.

How to use the tool

Add each HDD or SSD with a preset, or enter a custom capacity and drive type. Each selected drive remains an individual member of the configuration.
Switch between decimal GB/TB and binary GiB/TiB to change the display only; the stored byte capacities do not change.
Review every layout at once. Open its details to see group assumptions, capacity layers and how much of each drive is allocated or unused.
Copy the configuration link to bookmark or share the drive selection and display mode. The state is stored in the URL, not on a server.

Useful applications

Compare how mixed drive sizes affect conventional RAID arrays and tiered SHR estimates before choosing hardware.
Check the capacity and fault-tolerance trade-offs among RAID 5, RAID 6, nested layouts, ZFS mirrors and RAIDZ.
Explain why the capacity printed on drive labels differs from binary operating-system units and from the usable array capacity.

Notes and limitations

One decimal TB is 1,000,000,000,000 bytes. One binary TiB is 1,099,511,627,776 bytes; changing the display mode does not alter the underlying capacity.
Raw capacity is the sum of the selected drives. Usable capacity is the modeled array space for data. Protection capacity is the drive-equivalent space assigned to parity or mirror copies. Unused capacity is selected raw space that the modeled layout does not use.
The calculator estimates RAID or vdev capacity before filesystem, operating-system, vendor system-partition, swap, metadata, or reserved-space overhead. It does not predict the exact free space shown by a particular NAS or filesystem.
SHR and SHR-2 are Synology-specific. Their layer estimates use the rules stated in each layout's details and may differ from a particular NAS model, supported drive set, DSM release, or vendor calculator.
RAID provides availability against some drive failures, but it is not a replacement for an independent backup. Keep another recoverable copy of important data.

Frequently asked questions

Why is some capacity unused?

Many arrays use only a common drive-size band so every member can participate in each stripe or mirror. Larger drives may have a tail that does not fit the selected layout; nested groups can also leave capacity unused when their usable sizes differ.

What is the difference between TB and TiB?

TB uses decimal units: 1 TB is 10^12 bytes. TiB uses binary units: 1 TiB is 2^40 bytes. The display toggle changes labels and numbers, not the byte count used for calculations.

Why can SHR use mixed drive sizes differently?

Synology describes SHR as dividing drives into capacity chunks that can form multiple RAID arrays. This calculator models those bands as RAID 5 or RAID 1 layers for SHR-1 and RAID 6 layers for SHR-2 when enough drives remain. The exact result can depend on the NAS and DSM version.

Does this calculator include filesystem overhead?

No. It estimates RAID or vdev capacity before filesystem, operating-system, vendor partitions, swap, metadata and reserved space.

Can RAID replace a backup?

No. RAID redundancy can help a system stay available after supported drive failures, but it does not provide an independent historical copy against deletion, corruption, theft or other loss.

Why can RAID 10 tolerate more than one failure in some cases?

Each mirror pair has an independent copy. Failures in different pairs can be tolerated, while losing both drives in any one pair loses that pair's data. The result shows the pairings used by this model.

How are RAID 50 and RAID 60 grouped here?

Each uses exactly two equal-count groups: two RAID 5 groups for RAID 50 and two RAID 6 groups for RAID 60. Drives are sorted by capacity and alternated between groups; the grouping is shown in the result details.

1Choose your drives