StarWind Virtual SAN for vSphere inline deduplication is performed on the persistant storage layer (XFS partition with inline deduplication enabled on which StarWind devices are located).

Microsoft Windows Server native deduplication and compression can be set for StarWind virtual devices formatted as NTFS.

Windows Server 2019 Deduplication only happens in the persistent data layer and not in the cache. The cache is not accessible from the file system and so deduplication cannot be applied to it.