Get-S2DCacheTierInfo¶

Analyzes the S2D cache tier configuration, classifies cache vs capacity disks, computes the cache-to-capacity ratio, and detects all-flash software cache configurations.

Syntax¶

Get-S2DCacheTierInfo [[-CimSession] <CimSession>]

Parameters¶

Parameter	Type	Description
`-CimSession`	`CimSession`	Override the module session CimSession.

Output¶

Returns S2DCacheTier — a single object describing the cache tier.

Property	Type	Description
`CacheMode`	`string`	`ReadWrite`, `ReadOnly`, `WriteOnly`, or `No Cache`
`IsAllFlash`	`bool`	`$true` when no HDD or Unknown media types are present
`SoftwareCacheEnabled`	`bool`	`$true` on all-flash clusters (software write-back cache)
`CacheDiskCount`	`int`	Number of physical cache disks identified
`CacheDiskModel`	`string`	Most common cache disk model
`CacheDiskSize`	`S2DCapacity`	Largest cache disk size (TiB + TB)
`CacheToCapacityRatio`	`double`	Cache disk count ÷ capacity disk count
`CacheState`	`string`	`Active`, `Degraded`, or `None`
`WriteCacheSizeBytes`	`int64`	Write cache size from `ClusterS2D` settings

Cache Architecture Modes¶

Hybrid (NVMe/SSD over HDD)¶

The classic S2D cache configuration: faster media (NVMe or SSD) serves as a read/write cache for slower capacity drives (SSD or HDD). S2DCartographer identifies cache disks by Usage = Journal or by being the highest-ranked media type in the pool.

CacheMode:   ReadWrite
IsAllFlash:  False
CacheDiskCount: 2 (per node × 4 nodes = 8 total)
CacheToCapacityRatio: 0.5

All-Flash / All-NVMe¶

When all drives are NVMe or SSD, S2D does not use a physical cache/capacity split. Instead, it enables a software write-back cache across all drives. S2DCartographer detects this automatically:

IsAllFlash = $true — no HDD or Unknown media found
SoftwareCacheEnabled = $true — set from ClusterS2D.CacheEnabled or forced when all-flash is detected
CacheDiskCount = 0 — no dedicated cache devices

All-NVMe is the Azure Local default

Most Azure Local HCI configurations validated by Microsoft use all-NVMe drives. On these clusters, the software write-back cache is the only cache mechanism — Get-S2DCacheTierInfo will report IsAllFlash = $true and SoftwareCacheEnabled = $true with no physical cache disks.

CacheState Values¶

State	Meaning
`Active`	All cache disks are healthy, or software cache is enabled
`Degraded`	One or more cache disks are in a non-Healthy state
`None`	No cache tier and no software cache detected

A Degraded cache tier dramatically reduces write performance and may increase the risk of data loss if the cluster sustains additional failures. The CacheTierHealth check in Get-S2DHealthStatus flags this as a warning.

CIM Sources¶

Get-PhysicalDisk                 # disk classification (media type, Usage)
Get-ClusterS2D                   # software cache settings (CacheEnabled, CacheMode)

The function reuses physical disk data from $Script:S2DSession.CollectedData['PhysicalDisks'] when available, avoiding a redundant Get-PhysicalDisk query.

Session Behavior¶

Results are cached in $Script:S2DSession.CollectedData['CacheTier']. Get-S2DHealthStatus reads from this cache for the CacheTierHealth check.

Examples¶

# Cache tier summary
Get-S2DCacheTierInfo | Select-Object CacheMode, IsAllFlash, SoftwareCacheEnabled, CacheDiskCount, CacheState

# All-NVMe check
$cache = Get-S2DCacheTierInfo
if ($cache.IsAllFlash) {
    "All-flash cluster. Software cache: $($cache.SoftwareCacheEnabled)"
} else {
    "Hybrid cluster. Cache disks: $($cache.CacheDiskCount), ratio: $($cache.CacheToCapacityRatio):1"
}

# Cache disk inventory
Get-S2DPhysicalDiskInventory | Where-Object Role -eq 'Cache' | Format-Table NodeName, FriendlyName, Size, HealthStatus

Troubleshooting¶

CacheDiskCount is 0 on a hybrid cluster

If you expect physical cache disks but see CacheDiskCount = 0, the cache disks may not be classified correctly. Check that Get-S2DPhysicalDiskInventory shows some disks with Role = Cache or Usage = Journal.

On all-NVMe clusters this is expected — CacheDiskCount = 0 with SoftwareCacheEnabled = $true is correct.

WriteCacheSizeBytes is 0

WriteCacheSizeBytes is sourced from Get-ClusterS2D. On clusters where Get-ClusterS2D is unavailable (e.g., non-domain-joined management machines without RSAT), this property will be 0 even if the cluster has an active write cache. The IsAllFlash and CacheState properties are still computed from disk data.