Minor Description
Issue relates to:
http://docs.couchbase.com/couchbase-manual-2.5/cb-admin/#viewing-cluster-summary
I was working through a support case and trying to explain the cluster overview free space and usable free space.
The following statement is from out documentation. After code review of ns_server I concluded that this is incorrect.
Usable Free Space:
The amount of usable space for storing information on disk. This figure shows the amount of space available on the configured path after non-Couchbase files have been taken into account.
The correct statement should be
Usable Free Space:
The amount of usable space for storing information on disk. This figure is calculated from the node with least amount of available storage in the cluster. The final value is calculated by multiplying by the number of nodes in the cluster.
This change is important as it is important for users to understand why Usable Free Space can be less than Free Space. The cluster considers all nodes to be equal. If you actually have a "weak" node in the cluster, e.g. one with a small disk, then the cluster nodes all have to ensure they keep storage under the weaker nodes limits, else for example we can never failover to the weak node as it cannot take on the job of a stronger node. When Usable Free Space is less than Free space, the user may actually want to see why a node has less storage available.