Volumes

The volume planner converts logical planned sizes into two different numbers:

• Calculator TB: the logical size used by Surveyor for planning math.
• WAC GB: the floor-rounded value you actually type into Windows Admin Center or New-Volume -Size.

The conversion logic lives in src/engine/volumes.ts.

Why Surveyor shows two sizes

Storage planning breaks if you use the logical planner number directly in Windows Admin Center. WAC expects a binary GB value and rounds internally. If you over-specify the size, volume creation can fail.

Surveyor handles that by converting this way:

plannedSizeTB -> plannedSizeTB * 1024 -> floor() -> WAC GB

Pool footprint vs logical size

Each volume consumes more pool capacity than its logical size depending on resiliency:

• Two-way mirror: logical size / 0.5
• Three-way mirror: logical size / 0.333...
• Dual parity: logical size / factor based on node count
• Nested two-way mirror: logical size / 0.25

That pool-footprint calculation is why volume totals can exceed effective usable capacity even when the sum of logical TB still looks reasonable.

Guidance

• Use the WAC GB column when creating volumes.
• Keep individual volumes at or below 64 TB.
• Prefer a volume count that is a multiple of node count for balanced slab distribution.
• Keep overall utilization below 70% so S2D retains rebuild headroom.