Appendix C. Terminology  807 In most cases, the volume that contains a production copy of the data and that an application  accesses. See also “Auxiliary volume” on  page 796, and “Relationship” on page 810. Metro Mirror Global is a cascaded solution where Metro Mirror synchronously copies data to  the target site. This Metro Mirror target is the source volume for Global Mirror that  asynchronously copies data to a third site. This solution has the potential to provide disaster  recovery with no data loss at Global Mirror distances when the intermediate site does not  participate in the disaster that occurs at the production site. 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. A mirrored volume is a single virtual volume that has two physical volume copies. The primary  physical copy is known within the SVC as  copy 0  and the secondary copy is known within the  SVC as  copy 1 . An SVC node is a hardware entity that provides virtualization, cache, and copy services for  the cluster. The SVC nodes are deployed in pairs that are called I/O Groups. One node in a  clustered system is designated as the configuration node.  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. 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. 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 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 . Master volume Metro Global Mirror Metro Mirror Mirrored volume Node Node canister Node rescue NPIV Object Storage