Path Connections; Remote Mirror And Copy - IBM TotalStorage DS8000 User Manual

Path connections

Before you can create source and target remote mirror and copy copy pair
relationships, you must establish logical paths between a logical subsystem (LSS)
in a source storage unit and an LSS in a target storage unit.
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 unit 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 unit uses a worldwide port name (WWPN) to communicate with the target
storage unit. 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 bi-directional
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 a FCP interface can accommodate simultaneous data transfers, it does have
limited bandwidth. To distribute workload evenly to all available paths, the storage
unit 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.

Remote Mirror and Copy

Remote mirror and copy is a storage server feature that constantly updates a target
copy of a volume so that it matches changes that were made to its associated
source volume.
The remote mirror and copy feature is a hardware solution that enables the
mirroring of data from one site (the local site) and its associated volumes (source
volumes) to a second storage unit at another site (the recovery or remote site) and
its volumes (target volumes).
Note: Remote mirror and copy was referred to as Peer-to-Peer Remote Copy
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(PPRC) in earlier documentation for the IBM TotalStorage Enterprise Storage
Server. Currently, the remote mirror and copy feature name is used
generically for all methods of synchronous and asynchronous methods. In