Appendix C. Terminology 777
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 782.
Flash drive
A data storage device that uses solid-state memory to store persistent data.
Flash module
A modular hardware unit that contains flash memory, one or more flash controllers, and 
associated electronics.
Front end and back end
The IBM Storwize V7000 takes MDisks to create pools of capacity from which volumes are 
created and presented to application servers (hosts). The volumes that are presented to the 
hosts are in the front end of IBM Storwize V7000. 
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 V7000. 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).
Hop
One segment of a transmission path between adjacent nodes in a routed network.
Host bus adapter
A host bus adapter (HBA) is an interface card that connects a server to the SAN environment 
through its internal bus system, for example, PCI Express. Typically it is referred to the Fibre 
Channel adapters.
Host ID
A host ID is a numeric identifier that is assigned to a group of host FC ports or internet Small 
Computer System Interface (iSCSI) host names for LUN mapping. For each host ID, SCSI IDs 
are mapped to volumes separately. The intent is to have a one-to-one relationship between 
hosts and host IDs, although this relationship cannot be policed.
Host mapping
Host mapping refers to the process of controlling which hosts have access to specific 
volumes within a cluster. Host mapping is equivalent to LUN masking.