--- /dev/null
+Introduction
+------------
+
+[NOTE]
+I am leaving the introductory content here for now, but it is the last
+thing that should be written. The following is just a very early
+sketch, and will be revised entirely once the rest of the content has
+begun to shape up.
+
+The Lustre parallel file system provides a global POSIX namespace for
+the computing resources of a data center. Lustre runs on Linux-based
+hosts via kernel modules, and delegates block storage management to
+the back-end servers while providing object-based storage to its
+clients. Servers are responsible for both data objects (the contents
+of actual files) and index objects (for directory information). Data
+objects are gathered on Object Storage Servers (OSSs), and index
+objects are stored on Metadata Servers (MDSs). Each back-end
+storage volume is a target with Object Storage Targets (OSTs) on OSSs,
+and Metadata Targets (MDTs) on MDSs. Clients assemble the
+data from the MDTs and OSTs to present a single coherent
+POSIX-compliant file system. The clients and servers communicate and
+coordinate among themselves via network protocols. A low-level
+protocol, LNet, abstracts the details of the underlying networking
+hardware and presents a uniform interface, originally based on Sandia
+Portals <<PORTALS>>, to Lustre clients and servers. Lustre, in turn,
+layers its own protocol atop LNet. This document describes the Lustre
+protocol.
+
+Lustre runs across multiple hosts, coordinating the activities among
+those hosts via the exchange of messages over a network. On each host,
+Lustre is implemented via a collection of Linux processes (often
+called "threads"). This discussion will refer to a more formalized
+notion of 'processes' that abstract some of the thread-level
+details. The description of the activities on each host comprise a
+collection of 'abstract processes'. Each abstract process may be
+thought of as a state machine, or automaton, following a fixed set of
+rules for how it consumes messages, changes state, and produces other
+messages. We speak of the 'behavior' of a process as shorthand for the
+management of its state and the rules governing what messages it can
+consume and produce. Processes communicate with each other via
+messages. The Lustre protocol is the collection of messages the
+processes exchange along with the rules governing the behavior of
+those processes.
+
git://git.whamcloud.com / doc / protocol.git / blobdiff