Appendix C. Terminology 773
Clustered system (Storwize V7000)
A clustered system, which was known as a cluster, is a group of up to eight IBM Storwize 
V7000 canisters (two in each system) that presents a single configuration, management, and 
service interface to the user.
Cold extent
A cold extent is an extent of a volume that does not get any performance benefit if it is moved 
from a hard disk drive (HDD) to a Flash disk. A cold extent also refers to an extent that needs 
to be migrated onto an HDD if it is on a Flash disk drive.
Compression
Compression is a function that removes repetitive characters, spaces, strings of characters, 
or binary data from the data that is being processed and replaces characters with control 
characters. Compression reduces the amount of storage space that is required for data.
Compression accelerator
A compression accelerator is hardware onto which the work of compression is offloaded from 
the microprocessor.
Configuration node
While the cluster is operational, a single node in the cluster is appointed to provide 
configuration and service functions over the network interface. This node is termed the 
configuration node. This configuration node manages the data that describes the 
clustered-system configuration and provides a focal point for configuration commands. If the 
configuration node fails, another node in the cluster transparently assumes that role.
Consistency Group
A Consistency Group is a group of copy relationships between virtual volumes or data sets 
that are maintained with the same time reference so that all copies are consistent in time. A 
Consistency Group can be managed as a single entity.
Container
A container is a software object that holds or organizes other software objects or entities.
Contingency capacity
For thin-provisioned volumes that are configured to automatically expand, the unused real 
capacity that is maintained. For thin-provisioned volumes that are not configured to 
automatically expand, the difference between the used capacity and the new real capacity.
Copied state
Copied is a FlashCopy state that indicates that a copy was triggered after the copy 
relationship was created. The Copied state indicates that the copy process is complete and 
the target disk has no further dependency on the source disk. The time of the last trigger 
event is normally displayed with this status.
Counterpart SAN
A counterpart SAN is a non-redundant portion of a redundant SAN. A counterpart SAN 
provides all of the connectivity of the redundant SAN, but without the 100% redundancy. IBM 
Storwize V7000 canisters are typically connected to a “redundant SAN” that is made up of 
two counterpart SANs. A counterpart SAN is often called a SAN fabric.