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Aggregate Sizing Calculator

Estimate usable capacity for an ONTAP aggregate: raw disk size and count → RAID parity → WAFL/metadata overhead → snapshot reserve → storage efficiency.

Raw disk size (TiB) Number of disks (total, incl. spares) RAID type Hot spares RAID group size (disks per group, typical default 24) Aggregate overhead — WAFL/metadata % (typically ~10) Snapshot reserve % (ONTAP default 5) Volume efficiency factor (1.0 = none, 2.0 = typical mixed, 4.0 = VDI/backup-heavy)

Enter disk size and disk count.

Model: data disks = total − spares; groups = ⌈data / group size⌉; parity = RAID parity × groups; usable = raw × (data − parity) × (1 − overhead/100); then × (1 − snapshot/100) for live data; × efficiency for effective capacity.

How to use the result The first number is physical usable capacity. The "live data" number is what you can actually fill with client data while keeping snapshot headroom. The "effective" number is what storage efficiency might buy you — treat it as workload-dependent upside, not a guarantee.

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