Understanding usable capacity in a vSAN cluster
Raw drive capacity is not the same as space available to virtual machines in a distributed storage cluster. Protection policies, layout, metadata, operational reserves and rebuild requirements all affect usable capacity.
Request a documented capacity estimate
- Identify the host and disk configuration, software version and storage policy proposed for each workload.
- Confirm the failures-to-tolerate target and the supported data-protection layout for that configuration.
- Allow headroom for rebuilds, maintenance, snapshots and future growth instead of planning to fill the cluster.
- Separate application capacity requirements from optimistic assumptions about compression or deduplication savings.
Exact usable capacity must be calculated for the quoted design; it cannot be inferred reliably from a generic percentage. Storage redundancy also does not replace an independent backup. Ask us to review policy and capacity before a large migration or snapshot-heavy change.
