IBM General Parallel File System for AIX: Data Management API Guide

Glossary

B

block utilization

The measurement of the percentage of used subblocks per allocated blocks.

C

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 the Group Services component of PSSP, 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 publicationSystem 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.

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:

1. Processes changes to the state or description of the file system. These include:
   • Adding disks
   • Changing disk availability
   • Repairing the file system
2. Controls which regions of disks are allocated to each node, allowing effective parallel allocation of space.
3. Controls Token Management.
4. 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).

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.

i-node

The internal structure that describes an individual file to AIX. An i-node 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 i-node is required for each file.

J

journaled file system (JFS)

The local file system within a single instance of AIX.

L

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 i-nodes, 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.

N

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 complex.

P

primary server

When physical disks are connected to two nodes (twin-tailed), this is the node that normally maintains and controls local access to the disk.

Q

quorum

The minimum number of nodes that must be running in order for the GPFS daemon to start. This is one plus half of the number of nodes in the GPFS nodeset.

quota

The amount of disk space and number of i-nodes 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

RAID

Redundant Array of Independent Disks. A set of physical disks that are 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 server

The second node connected to a twin-tailed disk. This node assumes control of local access if the primary server fails.

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.

source node

The node on which a data management event is generated.

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