Path connections

Before you can create source and target remote mirror and copy pair relationships, you must establish logical paths between a logical subsystem (LSS) in a source storage system and an LSS in a target storage system.

When you implement a remote mirror and copy configuration, the definition of paths that remote mirror and copy uses is an important consideration. To establish paths, you must have Fibre Channel Protocol (FCP) adapters on both the source and target storage system for the peer-to-peer links. Paths are required for communicating between volume pairs and for copying data from a source volume to a target volume.

You can establish FCP paths to connect to a source LSS and a target LSS that contain count-key-data (CKD) or fixed block (FB) volumes. The requirement is that both the source LSS and target LSS must contain the same type of volumes.

You can define from one to eight FCP paths, depending on the capability of the LSS, from a single source site LSS to a specific target site LSS.

When you establish remote mirror and copy paths over FCP links, the source storage system uses a worldwide port name (WWPN) to communicate with the target storage system. The worldwide node name (WWNN) and system adapters identification (SAID) of the source and destination adapters are used to generate a WWPN. A WWPN consists of exactly 16 hexadecimal digits. The hexadecimal characters are 0–9, a–f, and A–F. The values for the WWNN and the WWPN must be unique.

With FCP, a single Fibre Channel link between two ports enables bidirectional remote mirror and copy operations. This means that it is possible to send and receive data in both directions simultaneously. For example, one link can have a path that is established in one direction and then have another path that is established in another direction at the same time, on the same physical path.

While an FCP interface can accommodate simultaneous data transfers, it does have limited bandwidth. To distribute workload evenly to all available paths, the storage system monitors the overall workload on each port and selects paths that are determined by the size of the data transfer, the available bandwidth available on each FCP port, and the number of data transfers, currently processing on each port. Selecting paths in this manner ensures good response time and overall system throughput.