Examining PPRC configuration options

Peer-to-peer remote copy allows mixed use of ESCON® and FCP types based on the following criteria: ther

An LSS to LSS pairing — you can only have one type of path, ESCON or FCP.
Paths for a source or target LSS can be mixed, as long as the different paths do not involve the same source and target LSSs.

You can define from one to eight ESCON or FCP paths, depending on the capability of the logical subsystem, from a single primary site logical subsystem to a specific recovery site logical subsystem. You can also attach up to Start of change

recovery site logical subsystems to each primary site logical subsystem. Therefore, a total of Start of change

128

paths can be defined between a single primary site logical subsystem and Start of change

recovery site logical subsystems. Figure 1 shows examples of possible ESCON path configurations between PPRC primary and recovery logical subsystems systems. Figure 2 shows an example of a configuration using FCP and ESCON.

Figure 1. PPRC ESCON path options

PPRC ESCON path options. The storage control on the primary site has a single path to each of three storage controls on the recovery site, and 4 paths to a fourth storage control on the recovery site.

A single storage subsystem at the recovery site can be linked to as many primary site logical subsystems as there are logical channels and devices available. A large cache and NVS help the recovery site logical subsystem to accept the copy workloads from multiple primary site logical subsystems.

You can use existing ESCON or FCP paths, or add other dedicated paths. ESCON paths can include an ESCON Director (ESCD) or Directors, or 9036 ESCON Remote Channel Extenders to provide configuration flexibility. FCP paths can be through fiber channel switch to provide configuration flexibility. PPRC over Fibre Channel allows a reduction in PPRC link infrastructures by a 4 to 1 ratio.

Note: You might have bandwidth restrictions using ESCON or FCP, if so, consider using the PPRC extended distance feature.Managing PPRC extended distance mode.

With FCP, a single fibre channel link between two ESS Model 800 ports enables bi-directional PPRC. This means that it is possible for data to travel in both directions simultaneously. For example, one link can have a PPRC path that is established in one direction and then have another PPRC path that is established in another direction at the same time, on the same physical path.

While a FCP interface can accommodate simultaneous data transfers, it does have limited bandwidth. To distribute workload evenly to all available paths, the ESS 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.

Figure 2. ESCON and FCP configuration