Fulfils the witness role in stretched and two-node vSAN clusters, as either a host or an appliance. No extra licence or subscription is needed, but unrelated workloads must not run on it.
Also called witness host, witness appliance.
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In the Ultra Transcenders books
Each book explains vSAN witness in context, with comparison tables and the common traps.
Terms in this definition
- Witness
Nutanix's preferred way of handling metro failures. Decisions are automatic, split brain is avoided, and a lost site is distinguished from a broken network link.
- Role
How an actor normally or expectedly behaves, or the part a person takes in a process. A single actor may hold more than one role.
- vSAN
VMware's software-defined storage, which combines local devices across a cluster's ESX hosts into one shared datastore. Available as OSA or ESA, VCF can use it as principal storage.
- Licence
What entitles one particular user to the services a subscription offers. Each product licence is made up of several service plans (one per app or service), and before giving it to someone an admin has to record that user's usage location.
- subscription
Entitlement bought for a product under VCF 9.0 licensing, carrying a set capacity. Where active ones share the same site, unit and product, their capacity is combined into licences, which are then allocated to vCenters.
Related terms
- two-node vSAN cluster
Two vSAN hosts on one site, supported by a witness host located somewhere else. If vSphere HA is in use, admission control has to reserve 50% or more of both CPU and memory.
- witness appliance
Two-node and stretched vSAN clusters can use this as their witness host. It is an ESX VM that comes ready-built in OVA form, with ESA and OSA each having their own image.
- witness host
Sits at a third site in a two-node or stretched vSAN cluster, supplying quorum and holding metadata instead of customer data. You can use either a physical machine or the witness appliance.
- witness traffic separation
Stretched vSAN deployments can give the witness its own VMkernel adapter for its traffic. That spares the witness host a second interface and removes any need to route between the data network and the witness site.