Software vSAN: Because data encryption is performed at the end of the write path, storage efficiency mechanisms are not impaired.
Software Hytrust: Because HyTrust DataControl is an end-to-end solution, encryption is performed at the start of the write path and some efficiency mechanisms (eg. deduplication and compression) are effectively negated.
VMware, vSAN [SDS]/7.0 U1, Enterprise
Data Encryption Efficiency Impact, Security, Data Services