Get-S2DCapacityWaterfall

Computes the complete 7-stage capacity accounting pipeline from raw physical disk capacity through resiliency overhead to final usable VM space.

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Syntax

Get-S2DCapacityWaterfall

No parameters. All inputs are sourced from the module session cache — the function automatically runs prerequisite collectors if their data is not already cached.

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Prerequisites

Get-S2DCapacityWaterfall depends on data from three other collectors. It runs them automatically if needed:

1. Get-S2DPhysicalDiskInventory — capacity disk sizes, largest drive, node count
2. Get-S2DStoragePoolInfo — pool total size and free space
3. Get-S2DVolumeMap — volume footprints and infrastructure volume classification

To run collectors explicitly in advance:

Connect-S2DCluster -ClusterName "c01-prd-bal" -Credential $cred
Get-S2DPhysicalDiskInventory | Out-Null
Get-S2DStoragePoolInfo       | Out-Null
Get-S2DVolumeMap             | Out-Null
$wf = Get-S2DCapacityWaterfall

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Output

Returns S2DCapacityWaterfall — a single object with top-level summary properties and a Stages array.

Top-level properties

Property	Type	Description
Stages	S2DWaterfallStage[]	The 7 pipeline stages (see below)
RawCapacity	S2DCapacity	Stage 1 total (sum of capacity-tier disk bytes)
UsableCapacity	S2DCapacity	Stage 7 total (final usable capacity)
ReserveRecommended	S2DCapacity	Recommended reserve: min(NodeCount, 4) × LargestDrive
ReserveActual	S2DCapacity	Actual free pool space
ReserveStatus	string	Adequate, Warning, or Critical
IsOvercommitted	bool	Whether OvercommitRatio > 1.0
OvercommitRatio	double	From StoragePool.OvercommitRatio
NodeCount	int	Node count used in reserve calculation
BlendedEfficiencyPercent	double	Average resiliency efficiency across workload volumes

Stage object properties

Property	Type	Description
Stage	int	Stage number (1–7)
Name	string	Stage label
Size	S2DCapacity	Remaining capacity at this stage
Delta	S2DCapacity	Bytes consumed vs previous stage ($null if none)
Description	string	Human-readable explanation of what changed
Status	string	OK — all stages are always OK; reserve health is on ReserveStatus only

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The 7 Stages

flowchart LR
    S1["Stage 1\nRaw Physical"] --> S2["Stage 2\nVendor Label"]
    S2 --> S3["Stage 3\nPool Overhead"]
    S3 --> S4["Stage 4\nReserve"]
    S4 --> S5["Stage 5\nInfra Volume"]
    S5 --> S6["Stage 6\nAvailable"]
    S6 --> S7["Stage 7\nUsable Capacity"]

Stage	Name	What changes
1	Raw Physical	Sum of all capacity-tier disk bytes (cache disks excluded)
2	Vendor Label (TB)	Display stage: shows vendor TB label vs Windows TiB. No bytes change.
3	Pool (after overhead)	Actual pool total size — captures ~0.5–1% metadata overhead
4	After Reserve	Subtracts min(NodeCount, 4) × LargestCapacityDrive
5	After Infra Volume	Subtracts Azure Local infrastructure volume footprint
6	Available	Pool space available for workload volumes
7	Usable Capacity	Stage 6 ÷ resiliency factor (e.g. ÷3 for three-way mirror). Pipeline terminus.

See Capacity Math for a full explanation of each stage.

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Reserve Status

Stage 4 computes a reserve status based on how actual free pool space compares to the recommended reserve:

Status	Condition
Adequate	ReserveActual ≥ ReserveRecommended
Warning	ReserveActual ≥ 50% of ReserveRecommended
Critical	ReserveActual < 50% of ReserveRecommended

The reserve recommendation follows the Microsoft S2D guidance: keep min(NodeCount, 4) capacity drive equivalents unallocated so the pool can rebuild after a drive or node failure.

CAUTION

Critical reserve status A Critical reserve means the pool cannot guarantee a complete rebuild after the loss of the largest drive. Immediately free pool space by shrinking or removing volumes.

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Session Behavior

Results are cached in $Script:S2DSession.CollectedData['CapacityWaterfall']. Calling Get-S2DCapacityWaterfall twice only queries the cluster once.

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Examples

# Full waterfall pipeline
$wf = Get-S2DCapacityWaterfall
$wf.Stages | Format-Table Stage, Name, Size, Delta, Status

# Summary
"Raw:        $($wf.RawCapacity.Display)"
"Usable:     $($wf.UsableCapacity.Display)"
"Reserve:    $($wf.ReserveStatus) — Actual: $($wf.ReserveActual.Display), Recommended: $($wf.ReserveRecommended.Display)"
"Efficiency: $($wf.BlendedEfficiencyPercent)%"

# Check reserve
if ($wf.ReserveStatus -ne 'Adequate') {
    Write-Warning "Reserve is $($wf.ReserveStatus): actual $($wf.ReserveActual.Display) vs recommended $($wf.ReserveRecommended.Display)"
}

# Stage 4 only
$wf.Stages | Where-Object Stage -eq 4 | Format-List

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Troubleshooting

WARNING

Stage 7 (Usable Capacity) is 0 TiB Usable capacity is zero when no workload volumes exist, or all volumes are classified as infrastructure. Check:

Get-S2DVolumeMap | Format-Table FriendlyName, IsInfrastructureVolume, Size

!!! note "Stage 2 shows no change" Stage 2 is informational only — it shows the vendor-labeled TB value alongside the Windows TiB value. The Size property does not change from Stage 1 to Stage 2 because the underlying bytes are the same. See TiB vs TB for an explanation of the discrepancy.

TIP

NodeCount affects reserve calculation The reserve uses min(NodeCount, 4) where NodeCount comes from $Script:S2DSession.Nodes.Count. If you call Get-S2DCapacityWaterfall without an active Connect-S2DCluster session (e.g., passing -CimSession directly to collectors), the node count falls back to the disk symmetry group count or 4. Use Connect-S2DCluster for accurate node counts.