HP XP P9000 Continuous Access Synchronous for Mainframe Systems User Guide

1 Continuous Access Synchronous Z overview
A Continuous Access Synchronous Z (Cnt AC S Z) system creates and maintains a mirror image
of a production volume at a remote location. Data in a Cnt Ac-S Z backup stays synchronized with
the data in the local XP P9500 storage system. This happens when data is written from the host to
the local storage system then to the remote storage system, through the Fibre Channel data path.
The host holds subsequent output until acknowledgement is received from the remote storage system
for the previous output.
Cnt Ac-S Z can be teamed with BC Z (BC Z) or Continuous Access Journal Z, on either or both
local and remote sites. These copy tools allow restoration from one or more additional copies of
critical data.
This guide provides instructions for planning, configuring, operating, maintaining, and
troubleshooting a Cnt Ac-S Z system.
How Continuous Access Synchronous Z works
A pair is created when you:
• Select a volume on the local storage system that you want to copy.
• Create or identify the volume on the remote system that will contain the copy.
• Connect the local and remote storage systems with a Fibre Channel (FC) channel data path.
• Copy all main volume data to the remote volume.
During a typical initial copy, all data written to the primary volume (P-VOL) is copied to the
secondary volume (S-VOL), ensuring that the secondary copy is a complete and consistent backup.
When a pair is suspended, writes to the main volume continue but are no longer copied to the
secondary side, and the pair is no longer synchronous.
• If a special S-VOL write option is enabled, the remote volume becomes available for read/write
access by secondary host applications. Otherwise the S-VOL remains as it was at the time of
the suspension.
• Changes to main and remote volumes (if applicable) are tracked by differential bitmaps until
the main and remote volumes are re-synchronized.
• When resynchronization takes place, only the changed data is transferred, reducing copy
time.
The XP P9500 storage system transfers control parameters and FBA-format data for consecutive,
updated records in a track using a single write operation. This eliminates the overhead that is
usually required for performing FBA-to-CKD and CKD-to-FBA conversions.
When Cnt Ac-S Z operations and other storage system processing are performed at the same time,
performance is affected.
To plan and implement a Cnt Ac-S Z system an understanding of its components is required. This
is provided in the following sections.
Typical components
A typical configuration consists of the following components. Many but not all require user setup.
• The local XP P9500 storage system is connected to a host. The remote storage system is
connected to the local system through Fibre Channel data paths. The remote system may be
8 Continuous Access Synchronous Z overview