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The parts of a cluster

This page names the parts that a MooseFS instance is made of, before any other chapter uses the names.

MooseFS keeps what a file is apart from what a file contains. The first two terms are the two halves of that split. A chunk is the piece of file data that the cluster stores, places, and protects as one thing. Metadata and namespace is everything else that a file system records: the tree, the attributes, and the record of where every chunk is stored.

Each half has a component that holds it. The Master Server holds the metadata and answers every operation on it. The Chunkservers hold the chunks on their disks. A Metalogger keeps a second copy of the metadata on a machine of its own. The Metalogger serves nothing from that copy.

Access to any of that goes through a client. The client is the module that speaks the MooseFS protocol for an application. The client usually presents the file system as a mount. Session and export covers whether a client is admitted at all, and what the Master Server keeps about that client afterwards.