2.2 vSAN Key Terminology
vSAN uses a number of terms that are good to define before proceeding:
• Each vSAN host contributing storage does so in the form of a “disk group”.
• A disk group is a combination of exactly one cache-tier SSD and one or more capacity-tier drives.
• The cache tier is used for write buffering and/or read caching.
• The capacity tier is used for long-term persistence and data at rest.
• vSAN object – Every element of the VM (home directory, VMDKs, snapshots, swap files) is an object in vSAN, not a file.
• vSAN Component – Objects are distributed constructs made of components.
o Components are the data and witnesses that allow the object to be assembled and deliver data to the end user (the VM).
• Witness – A witness is a metadata-only component. It exists to maintain quorum and to secure integrity during split-brain scenarios.