Appendix C. Terminology 781
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 V7000 as copy 0 and the secondary copy is 
known within the IBM Storwize V7000 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 with no valid software is installed on its hard disk drive can copy 
software from another node connected to the same Fibre Channel fabric.
NPIV
N_Port ID Virtualization (NPIV) 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 Cloud Object Storage 
organizes, manages, and stores 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.
Over provisioned
See “Capacity” on page 771.
Over provisioned ratio
See “Capacity” on page 771.
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.
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.