Appendix B. Terminology 825
Field-replaceable unit
Field-replaceable units (FRUs) are individual parts that are replaced entirely when any one of
the unit’s components fails. They are held as spares by the IBM service organization.
FlashCopy
FlashCopy refers to a point-in-time copy where a virtual copy of a volume is created. The
target volume maintains the contents of the volume at the point in time when the copy was
established. Any subsequent write operations to the source volume are not reflected on the
target volume.
FlashCopy mapping
A FlashCopy mapping is a continuous space on a direct-access storage volume, which is
occupied by or reserved for a particular data set, data space, or file.
FlashCopy relationship
See FlashCopy mapping.
FlashCopy service
FlashCopy service is a copy service that duplicates the contents of a source volume on a
target volume. In the process, the original contents of the target volume are lost. See also
“Point-in-time copy” on page 830.
Flash drive
A data storage device that uses solid-state memory to store persistent data.
Flash module
A modular hardware unit containing flash memory, one or more flash controllers, and
associated electronics.
Front end and back end
The IBM Storwize V5000 takes MDisks to create pools of capacity from which volumes are
created and presented to application servers (hosts). The MDisks are in the controllers at the
back end of Storwize V5000 and in the Storwize V5000 to the back-end controller zones. The
volumes that are presented to the hosts are in the front end of IBM Storwize V5000.
Global Mirror
Global Mirror (GM) is a method of asynchronous replication that maintains data consistency
across multiple volumes within or across multiple systems. Global Mirror is generally used
where distances between the source site and target site cause increased latency beyond
what the application can accept.
Global Mirror with change volumes
Change volumes are used to record changes to the primary and secondary volumes of a
remote copy relationship. A FlashCopy mapping exists between a primary and its change
volume and a secondary and its change volume.
Grain
A grain is the unit of data that is represented by a single bit in a FlashCopy bitmap (64 KiB or
256 KiB) in the IBM Storwize V5000. A grain is also the unit to extend the real size of a
thin-provisioned volume (32 KiB, 64 KiB, 128 KiB, or 256 KiB).
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