--- /dev/null
+[glossary]
+Glossary
+--------
+Here are some common terms used in discussing Lustre, POSIX semantics,
+and the protocols used to implement them.
+
+[glossary]
+back end file system::
+Storage on a server in support of the object store or of metadata is
+stored on the back end file system. The two available file systems are
+currently ldiskfs and ZFS.
+
+Client::
+A Lustre client is a computer taking advantage of the services
+provided by MDSs and OSSs to assemble a POSIX-compliant file system
+with its namespace and data storage capabilities.
+
+Distributed Lock Manager::
+The distributed lock manager (DLM, often referred to as the Lustre
+Distributed Lock Manager, or LDLM) is the service that enforces a
+consistent (cache-coherent) view of the data objects in the file
+system.
+
+early reply::
+A message returned in response to a request message that allows the
+target to extend timeout values without otherwise indicating the
+request has progressed.
+
+export::
+The term for the per-client shared state information held by a server.
+
+extent:: A range of offsets in a file.
+
+import::
+The term for the per-target shared state information held by a client.
+
+Inodes and Extended Attributes::
+Metadata about a Lustre file is encoded in the extended attributes of
+an inode in the back-end file system on the MDS. Some of that
+information establishes the stripe layout of the file. The size of the
+stripe layout information varies among Lustre file systems. The amount
+of space reserved for layout information is a small as possible given
+the maximum stripe count possible on the file system. Clients, servers,
+and the distributed lock manager will all need to be aware of this
+size, which is communicated in the 'ocd_ibis_known' filed of the
+'obd_connect_data' structure.
+
+LNet::
+A lower level protocol employed by PtlRPC to abstract the mechanisms
+provided by various hardware centric protocols, such as TCP or
+Infiniband.
+
+The Log Subsystem::
+
+Fixme:
+The log subsystem (LOG) is something I have no idea about right now.
+
+Logical Object Volume::
+The logical object volume (LOV) layer abstracts the targets on a server.
+
+Management Server::
+The Management Server (MGS) maintains an understanding of the other
+servers, targets, and client in the Lustre file system. It holds their
+identities and keeps track of disconnections and reconnections in
+order to support imperative recovery.
+
+Metadata Server::
+A metadata server (MDS) is a computer responsible for running the
+Lustre kernel services in support of managing the POSIX-compliant name
+space and the indices associating files in that name space with the
+locations of their corresponding objects. As of v2.4 there can be
+multiple MDSs in a Lustre file system.
+
+Metadata Target::
+A metadata target (MDT) is the service provided by an MDS that
+mediates the management of name space indices on the underlying file
+system hardware. As of v2.4 there can be multiple MDTs on an MDS.
+
+Object Based Disk::
+Object Based Disk (OBD) is the term used for any target, MDT or OST.
+
+Object Storage Server::
+An object storage server (OSS) is a computer responsible for running
+Lustre kernel services in support of managing bulk data objects on the
+underlying storage. There can be multiple OSSs in a Lustre file
+system.
+
+Object Storage Target::
+An object storage target (OST) is the service provided by an OSS that
+mediates the placement of data objects on the specific underlying file
+system hardware. There can be multiple OSTs on a given OSS.
+
+protocol::
+An agreed upon formalism for communicating between two entities, such
+as between two servers or between a client and a server.
+
+PtlRPC::
+The protocol (or set of protocols) implemented via RPCs that is (are)
+employed by Lustre to communicate between its clients and servers.
+
+Remote Procedure Call::
+A mechanism for implementing operations involving one computer acting
+on the behalf of another (RPC).
+
+server::
+A computer that provides a service. For example, management (MGS),
+Metadata (MDS), or object storage (OSS) services in support of a
+Lustre file system.
+
+target::
+Storage available to be served, such as an OST or an MDT. Also the
+service being provided.
+
+UUID:: A universally unique identifier.
git://git.whamcloud.com / doc / protocol.git / blobdiff