Placement and policies

This section describes which servers a chunk's copies and parts are placed on, and which settings decide the placement.

Storage Class evaluation covers the definition that governs a chunk at a given moment and when the archive rule moves the chunk to another storage state. Label expressions and matching covers how a definition is matched against the Chunkservers and what each labels mode does when too few of them match. Erasure Coding: part layout covers what changes when a chunk is kept as data parts and parity parts instead of whole copies. Preferred labels covers the only placement-like decision that a client makes on its own: which of the servers holding a chunk the client contacts first.

Three pages cover the settings around the placement itself. Class priority and export groups covers which class governs a chunk that several files share and which mounts may assign a class. Topology mapping and distance covers the number to which MooseFS reduces a network layout, and every decision that uses the number. How policies are applied covers how an object gets its class, trash retention, and extra attributes.