B. When you enable deduplication and compression on a vSAN cluster, all disk groups participate in data reduction through deduplication and compression. You can add a capacity disk to a disk group with enabled deduplication and compression. However, for more efficient deduplication and compression, instead of adding capacity disks, create a new disk group to increase cluster storage capacity. https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vsan.doc/GUID-AA72CA1D-803D-4D1D-87BB-E7D86EC947D2.html

I believe A is correct and if comes in exam i would flip coin between A and B :)

A is correct

Agreed, A is correct based on the criteria being asked for. Taken from VMware doco "vSAN can eliminate duplicate data blocks within each disk group, but not across disk groups" https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vsan.doc/GUID-2285B446-46BF-429C-A1E7-BEE276ED40F7.html

A and B are the only two possible answers as DD&C is only available on all flash configuration. I'm gona say A is correct as DD&C is performed per disk group so a single disk group will give a better DD ratio. I'm aware that best practice is always to have more than one disk group, for performance and redundancy (more fault domains) but the question does not mention best practice, only maximizing capacity. The article below does say to use more than one disk group, however it is in relation to performance. https://blogs.vmware.com/virtualblocks/2020/06/18/vsan-design-considerations-deduplication-and-compression/ In my opinion , and based purely on the wording of the question I think that answer A is correct.