- B
- block utilization
- The measurement of the percentage of used subblocks per allocated
blocks.
- C
- cluster
- A loosely-coupled collection of independent systems (nodes) organized into
a network for the purpose of sharing resources and communicating with each
other (see GPFS cluster).
- concurrent access
- Simultaneous access to a shared volume group or a raw disk by two or more
nodes. In this configuration, all the nodes defined for concurrent
access to a shared volume group are owners of the shared resources associated
with the volume group or raw disk.
If one of the nodes in a concurrent access environment fails, it releases
the shared volume group or disk, along with its resources. Access to
the shared volume group or disk is, however, continuously available, as long
as another node is up. Applications can switch to another server
immediately.
- Configuration Manager
- The GPFS node that selects File System Managers and determines whether
quorum exists. The oldest continuously operating node in the file
system group as monitored by Group Services, is automatically assigned as the
Configuration Manager.
- control data structures
- Data structures needed to manage file data and metadata cached in
memory. This includes hash tables and link pointers for finding cached
data, lock states and tokens to implement distributed locking, as well as
various flags and sequence numbers to keep track of updates to the cached
data.
- D
- Data Management API
- The interface defined by the Open Group's XDSM standard as described
in the publication System
Management: Data Storage Management (XDSM) API Common Application
Environment (CAE) Specification C429, The Open Group ISBN
1-85912-190-X.
- DFS
- Distributed File Service. A subset of the IBM Distributed Computing
Environment and sometimes referred to as Distributed File System in other
documentation.
- disk descriptor
- A disk descriptor defines how a disk is to be used within a GPFS file
system. Each descriptor must be in the form:
DiskName:::DiskUsage:FailureGroup
Where DiskName is the name of the disk. This must be the
virtual shared disk name.This must be the name of the concurrent
logical volume.This must be the network shared disk name.
DiskUsage tells GPFS whether data, metadata, or both are to be stored
on the disk. The FailureGroup designation indicates to GPFS
where not to place replicas of data and metadata. All disks
with a common point of failure should belong to the same failure group.
Since GPFS does not place replicated information on disks in the same failure
group, the availability of information is ensured even in the event of disk
failure.
- disposition
- The session to which a data management event is delivered. An
individual disposition is set for each type of event from each file
system.
- E
- event
- A message from a file operation to a data management application about the
action being performed on the file or file system. There are several
types of events, each used for a different type of action. The event is
delivered to a session according to the event disposition.
- F
- failover
- The assuming of server responsibilities by the node designated as backup
server, when the primary server fails.
- failure group
- A collection of disks that share common access paths or adaptor
connection, and could all become unavailable through a single hardware
failure.
- File System Manager
- There is one File System Manager per file system, which provides the
following services for all the nodes using the file system:
- Processes changes to the state or description of the file system.
These include:
- Adding disks
- Changing disk availability
- Repairing the file system
- Controls which regions of disks are allocated to each node, allowing
effective parallel allocation of space.
- Controls Token Management.
- Controls Quota Management.
- fragment
- The space allocated for an amount of data (usually at the end of a file)
too small to require a full block, consisting of one or more subblocks (one
thirty-second of block size).
- G
- GPFS cluster
- A subset of existing cluster nodes defined as being available for use by
GPFS file systems. The GPFS cluster is created via the mmcrcluster command. GPFS nodesets and file
systems are subsequently created after the mmcrcluster command has
been issued.
- GPFS cluster data
- The GPFS configuration data. In an SP environment, this data is
stored in the SDR. In an HACMP environment, this data is stored on the
primary and secondary GPFS cluster data servers as defined on the mmcrcluster command.
- H
- HACMP environment
- The operation of GPFS based on the High Availability Cluster
Multi-Processing for AIX/Enhanced Scalability (HACMP/ES) program
product.
- I
- IBM Virtual Shared Disk
- A subsystem that allows application programs executing on different nodes
access a raw logical volume as if it were local at each node.
- inode
- The internal structure that describes an individual file. An inode
contains file size and update information, as well as the addresses of data
blocks, or in the case of large files, indirect blocks that, in turn, point to
data blocks. One inode is required for each file.
- J
- journaled file system (JFS)
- The local file system within a single instance of AIX.
- L
- Low-Level Application Programming Interface (LAPI)
- LAPI is an IBM communication protocol design for the efficient exchange of
messages in a packet switched network. It provides both reliable and
efficient notification of message completion. It is optimized for
networks where dropped packets are rare. LAPI is supported over a
UDP/IP socket interface and performs similarly to the TCP/IP protocol.
- logical volume
- (1.) A collection of physical partitions organized into logical
partitions all contained in a single volume group. Logical volumes are
expandable and can span several physical volumes in a volume group.
(2.) A set of logical partitions, each of which is stored on one or
more physical partitions from one or more of the physical volumes of a given
volume group. A logical volume has a device name (of the form /dev/hdn)
and contains a single file system.
- Logical Volume Manager (LVM)
- Manages disk space at a logical level. It controls fixed-disk
resources by mapping data between logical and physical storage, allowing data
to be discontiguous, span multiple disks, replicated, and dynamically
expanded.
- M
- metadata
- Data structures that contain access information about file data.
These might include inodes, indirect blocks, and directories. These
data structures are used by GPFS but are not accessible to user
applications.
- metanode
- There is one metanode per open file. The metanode is responsible
for maintaining file metadata integrity. In almost all cases, the node
that has had the file open for the longest period of continuous time is the
metanode.
- mirroring
- The creation of a mirror image of data to be preserved in the event of
disk failure.
- multi-node quorum
- The type of quorum algorithm used for GPFS nodesets
of 3 nodes or more. This is defined as one plus half of the number of
nodes in the GPFS nodeset.
- multi-tailing
- Connecting a disk to multiple nodes.
- N
- Network File System (NFS)
- A distributed file system that allows users to access files and
directories located on remote computers and treat those files and directories
as if they were local. NFS allows different systems (UNIX or non-UNIX),
different architectures, or vendors connected to the same network, to access
remote files in a LAN environment as though they were local files.
- node number
- GPFS references node numbers in an environment specific manner. In
an SP environment, the node number is obtained from the SDR. In a
HACMP/ES cluster environment, the node number is obtained from the global
ODM.
- nodeset
- A GPFS nodeset is a group of nodes that all run the same level of GPFS
code and operate on the same file systems. You have the ability to
define more than one GPFS nodeset in the same SP partition or GPFS
cluster.
- P
- primary GPFS cluster data server
- In a GPFS cluster, this refers to the primary GPFS cluster data server
node for the GPFS configuration data.
- Q
- quorum
- The minimum number of nodes that must be running in order for the GPFS
daemon to start.
For all nodesets consisting of three or more nodes, the multi-node quorum algorithm applies defining quorum as one
plus half of the number of nodes in the GPFS nodeset.
For a two node nodeset, the single-node quorum
algorithm can be applied allowing the GPFS daemon to continue operation
despite the loss of the peer node.
- quota
- The amount of disk space and number of inodes assigned as upper limits for
a specified user or group of users.
- quota management
- In a quota-enabled configuration, the File System Manager node
automatically assumes the quota management responsibilities whenever GPFS is
started. Quota management involves the allocation of disk blocks to the
other nodes writing to the file system and comparison of the allocated space
to quota limits at regular intervals.
- R
- Redundant Array of Independent Disks (RAID)
- A set of physical disks that act as a single physical volume and use
parity checking to protect against disk failure.
- recovery
- The process of restoring access to file system data when a failure has
occurred. This may involve reconstructing data or providing alternative
routing through a different server.
- replication
- The practice of creating and maintaining multiple file copies to ensure
availability in the event of hardware failure.
- S
- SSA
- Serial Storage Architecture. An expanded storage adapter for
multi-processor data sharing in UNIX-based computing, allowing disk connection
in a high-speed loop.
- SCSI
- Small Computer Systems Interface. An adapter supporting attachment
of various direct-access storage devices.
- secondary GPFS cluster data server
- In a GPFS cluster, this refers to the backup server node for the GPFS
configuration data (see GPFS cluster data).
- session failure
- The loss of all resources of a data management session due to the failure
of the GPFS daemon on the session node.
- session node
- The node on which a data management session was
created.
- single-node quorum
- In a two node nodeset, use of the single-node quorum
algorithm allows the GPFS daemon to continue operating in the event only one
node is available. Use of this quorum algorithm is not valid if more
than two nodes have been defined in the nodeset.
- source node
- The node on which a data management event is generated.
- SP environment
- The operation of GPFS based on the PSSP and IBM Virtual Shared Disk
program products.
- stripe group
- The set of disks comprising the storage assigned to a file system.
- striping
- A method of writing a file system, in parallel, to multiple disks instead
of to single disks in a serial operation.
- subblock
- The smallest unit of data accessible in an I/O operation, equal to one
thirty-second of a data block.
- T
- token management
- A system for controlling file access in which each application performing
a read or write operation is granted exclusive access to a specific block of
file data. This ensures data consistency and controls conflicts.
Token management has two components: the token manager server,
located at the File System Manager node, and the token management function on
each node in the GPFS nodeset. The token management server controls
tokens relating to the operation of the file system. The token
management function on each node, including the File System Manager node,
requests tokens from the token management server.
- twin-tailing
- Connecting a disk to multiple nodes
- V
- virtual file system (VFS)
- A remote file system that has been mounted so that it is accessible to the
local user. The virtual file system is an abstraction of a physical
file system implementation. It provides a consistent interface to
multiple file systems, both local and remote. This consistent interface
allows the user to view the directory tree on the running system as a single
entity even when the tree is made up of a number of diverse file system
types.
- virtual shared disk
- The function that allows application programs executing at different nodes
of a system partition to access a raw logical volume as if it were local at
each of the nodes. In actuality, the logical volume is local at only
one of the nodes (the server node).
- virtual node (vnode)
- The structure which contains information about a file system object in an
virtual file system.
