Appendix B. Terminology 829
Metro Mirror
Metro Mirror (MM) is a method of synchronous replication that maintains data consistency
across multiple volumes within the system. Metro Mirror is generally used when the write
latency that is caused by the distance between the source site and target site is acceptable to
application performance.
Mirrored volume
A mirrored volume is a single virtual volume that has two physical volume copies. The primary
physical copy is known within the IBM Storwize V5000 as copy 0 and the secondary copy is
known within the IBM Storwize V5000 as copy 1.
Node canister
A node canister is a hardware unit that includes the node hardware, fabric and service
interfaces, and serial-attached SCSI (SAS) expansion ports. Node canisters are specifically
recognized on IBM Storwize products. In SVC all these components are spread within the
whole system chassis, so we usually do not consider node canisters in SVC, but just the node
as a whole.
Node rescue
The process by which a node that has no valid software installed on its hard disk drive can
copy software from another node connected to the same Fibre Channel fabric.
NPIV
NPIV or N_Port ID Virtualization is a Fibre Channel feature whereby multiple Fibre Channel
node port (N_Port) IDs can share a single physical N_Port.
Object Storage
Object storage is a general term that refers to the entity in which an Cloud Object Storage
(COS) organize, manage and store with units of storage or just
objects.
Oversubscription
Oversubscription refers to the ratio of the sum of the traffic on the initiator N-port connections
to the traffic on the most heavily loaded ISLs, where more than one connection is used
between these switches. Oversubscription assumes a symmetrical network, and a specific
workload that is applied equally from all initiators and sent equally to all targets. A
symmetrical network means that all the initiators are connected at the same level, and all the
controllers are connected at the same level.
Parent pool
Parent pools receive their capacity from MDisks. All MDisks in a pool are split into extents of
the same size. Volumes are created from the extents that are available in the pool. You can
add MDisks to a pool at any time either to increase the number of extents that are available
for new volume copies or to expand existing volume copies. The system automatically
balances volume extents between the MDisks to provide the best performance to the
volumes. See also “Child pool” on page 821.
Partnership
In Metro Mirror or Global Mirror operations, the relationship between two clustered systems.
In a clustered-system partnership, one system is defined as the local system and the other
system as the remote system.
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