GPFS: Administration and Programming Reference - IRA Home

Glossary
This glossary defines technical terms and
abbreviations used in GPFS documentation. If you
do not find the term you are looking for, refer to
the index of the appropriate book or view the IBM
Glossary of Computing Terms, located on the
Internet at: w3.ibm.com/standards/terminology.
B
backup NSD server. A node designated to perform
NSD disk access functions in the event that the primary
NSD server fails.
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 also “GPFS cluster” on page 381).
cluster configuration data files. The configuration
data that is stored on the cluster configuration servers.
configuration manager. The node that selects file
system managers and determines whether quorum
exists. The oldest continuously operating node in the file
system group is automatically assigned as the
configuration manager.
control data structures. Data structures needed to
manage file data and metadata cached in memory.
Control data structures include hash tables and link
pointers for finding cached data; lock states and tokens
to implement distributed locking; and various flags and
sequence numbers to keep track of updates to the
cached data.
D
Data Management Application Program Interface
(DMAPI). 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.
deadman switch timer. A kernel timer that ensures
that a node that has lost its disk lease and has
outstanding I/O requests cannot complete those
requests (and risk causing file system corruption). This
is achieved by panicking the kernel.
disk descriptor. A disk descriptor defines how a disk
is to be used within a file system. Each descriptor
supplied to the mmcrfs command must be in the form
(second, third and sixth fields reserved):
DiskName:::DiskUsage:FailureGroup::StoragePool
Each descriptor supplied to the mmcrnsd command
must be in the form:
DiskName:PrimaryServer:BackupServer:DiskUsage:
FailureGroup:DesiredName:StoragePool
DiskName
The block device name appearing in /dev for
the disk you want to define as an NSD.
Examples of disks accessible through a block
device are SAN-attached disks or virtual
shared disks. If a PrimaryServer node is
specified, DiskName must be the /dev name
for the disk device on the primary NSD server
node. Use the GPFS FAQ link at
http://publib.boulder.ibm.com/infocenter/clresctr/
index.jsp?topic=/com.ibm.cluster.infocenter.doc/
library.html for the latest supported disk types.
Note that GPFS provides some helper
commands to ease configuration of /dev disk
devices. For instance the mmcrvsd command
can configure a virtual shared disk and make it
accessible to nodes connected over a high
performance switch. The output disk descriptor
file from an mmcrvsd command can be used
as input to the mmcrnsd command since the
virtual shared disk names enumerated in that
file will appear as /dev block devices on switch
attached nodes.
PrimaryServer
The name of the primary NSD server node.
If this field is omitted, the disk is assumed to
be directly attached to all nodes in the cluster.
BackupServer
The name of the backup NSD server node.
If the PrimaryServer has been specified and
this field is omitted, it is assumed you do not
want failover in the event the PrimaryServer
fails. If a PrimaryServer has not been specified,
this field must also be omitted.
Disk Usage
What is to be stored on the disk:
dataAndMetadata
Indicates that the disk contains both
data and metadata. This is the default.
dataOnly
Indicates that the disk contains data
and does not contain metadata.
© Copyright IBM Corp. 1998, 2006 379