Deduplication and Compression are new features of Virtual SAN 6.2. Disabled by default, these features can be enabled by selecting the cluster, going to the Manage tab and selecting General.
Deduplication and compression can be enabled only as a unit, there is no way to enable one feature without the other.
Deduplication takes place when data is de-staged from the cache tier using a default 4k block.
Compression takes place immediately after deduplication and before data is written to the capacity tier. Data is compressed only if it can be reduced to 2k blocks or less. Otherwise, data is not compressed.
Is there a drawback?
Additional cpu cycles and reduced latency, mitigated that all the drives are flash devices.
Deduplication and compression only work with the All-FLASH architecture.