In versions prior to vSAN 6.0, witnesses are an element of every storage object. A witness does not contain data, only metadata (approximately 2 MB per witness object). The purpose of a witness is to serve as a tiebreaker when a failure in the cluster occurs and an availability decision must be made to enforce the failures to tolerate policy.

vSAN 6.0 introduces a slightly different way to manage how the cluster’s quorum is computed: each element has a number of votes which contributes to the final decision in the case of failure. It is possible for an object to be distributed in such a way as to not require the witness for the failures to tolerate decision.