Introduction
------------

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 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 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.

The remainder of the introduction presents several concepts that
illuminate the operation of the Lustre protocol. In
<<file-system-operations>> a subsection is devoted to each of several
semantic operations (setattr, statfs, ...). That discussion introduces
the RPCs of the Lustre protocol, to give an idea of how RPCs are used
to implement the file system. In <<lustre-rpcs>> each RPC of the
Lustre protocol is presented in turn.

include::client.txt[]

include::target.txt[]

include::rpc.txt[]

include::connection.txt[]

include::transno.txt[]

include::path_lookup.txt[]

include::lov_index.txt[]

include::grant.txt[]

include::ldlm.txt[]

include::llog.txt[]

include::security.txt[]