Expansion planning

Replace drives with a clear capacity checkpoint.

Larger disks do not always create usable space immediately. Model a simple, equal-size starting array first, then use the source links to check the exact appliance or filesystem workflow.

Expansion simulator

See when larger replacement drives change usable capacity.

Model one equal-size array before purchasing a batch of drives. The result is a planning checkpoint, not a substitute for the target platform’s own capacity rules.

Read the replacement guide →
Before replacements——
After this step——
Next decision

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Model boundary

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Replacement path

Each replacement, held against the same assumptions.

Replaced drivesModelled usable capacityWhat changes

Sources and scope

Last reviewed 2026-07-13. This page separates the decision it supports from the facts that still require a platform or model-specific check.

Applies to

An equal-size starting array where every replacement drive is the same larger capacity. It is most useful for planning a purchase sequence and spotting when a larger-drive upgrade may not create immediate usable space.

Does not cover

Mixed-drive capacity, vendor firmware behavior, ZFS vdev expansion, disk compatibility, rebuild duration, or whether a platform requires a separate expand action.

Synology drive replacement and expansion guidancePlatform-specific conditions for capacity changes after drive replacement.Open source ↗Synology RAID CalculatorCapacity estimation for supported Synology drive combinations.Open source ↗TrueNAS ZFS Capacity CalculatorZFS capacity, redundancy, and configuration-planning reference.Open source ↗