IBM Elastic Storage System 3200 Service Manual page 52

declustered array (DA)
A disjoint subset of the pdisks in a recovery group.
dependent fileset
A fileset that shares the inode space of an existing independent fileset.
DFM
See direct FSP management (DFM).
DHCP
See Dynamic Host Configuration Protocol (DHCP).
drawer control module (DCM)
Essentially, a SAS expander on a storage enclosure drawer.
Dynamic Host Configuration Protocol (DHCP)
A standardized network protocol that is used on IP networks to dynamically distribute such network
configuration parameters as IP addresses for interfaces and services.
E
Elastic Storage System (ESS)
A high-performance, GPFS NSD solution made up of one or more building blocks. The ESS software
runs on ESS nodes - management server nodes and I/O server nodes.
encryption key
A mathematical value that allows components to verify that they are in communication with the
expected server. Encryption keys are based on a public or private key pair that is created during the
installation process. See also file encryption key (FEK), master encryption key (MEK).
ESS
See Elastic Storage System (ESS).
environmental service module (ESM)
Essentially, a SAS expander that attaches to the storage enclosure drives. In the case of multiple
drawers in a storage enclosure, the ESM attaches to drawer control modules.
ESM
See environmental service module (ESM).
F
failback
Cluster recovery from failover following repair. See also failover.
failover
(1) The assumption of file system duties by another node when a node fails. (2) The process of
transferring all control of the ESS to a single cluster in the ESS when the other clusters in the ESS fails.
See also cluster. (3) The routing of all transactions to a second controller when the first controller fails.
See also cluster.
failure group
A collection of disks that share common access paths or adapter connection, and could all become
unavailable through a single hardware failure.
FEK
See file encryption key (FEK).
file encryption key (FEK)
A key used to encrypt sectors of an individual file. See also encryption key.
file system
The methods and data structures used to control how data is stored and retrieved.
file system descriptor
A data structure containing key information about a file system. This information includes the disks
assigned to the file system (stripe group), the current state of the file system, and pointers to key files
such as quota files and log files.
40 IBM Elastic Storage System 3200: Service Guide