HP XP7 Storage - Manual (Page 8)

1 Continuous Access Synchronous Z overview
A Continuous Access Synchronous Z system creates and maintains a mirror image of a production
volume at a remote location. Data in a Continuous Access Synchronous Z backup stays synchronized
with the data in the primary XP7 Storage storage system. This happens when data is written from
the host to the primary storage system then to the secondary storage system, via the Fibre Channel
data path. The host holds subsequent output until acknowledgement is received from the secondary
storage system for the previous output.
This guide provides instructions for planning, configuring, operating, maintaining, and
troubleshooting a Continuous Access Synchronous Z system.
Important: Procedures in this manual are tailored to the Remote Web Console (RWC) GUI. When
using this GUI, “Local Storage System” displays for the system you have accessed on the RWC
server.
As a result, if you access the remote site’s RWC server, the GUI displays information for the pair’s
remote (secondary) system under “Local Storage System”. Likewise, the GUI in this case identifies
the storage system connecting to the accessed system as the “Remote Storage System”.
However, this manual uses the terms ”primary storage system” or “primary system” for the storage
system in which the primary volume (P-VOL) is located in the local site, and “secondary storage
system” or “secondary system” for the storage system in which the secondary volume (S-VOL) is
located in the remote site, unless otherwise noted.
How Continuous Access Synchronous Z works
A pair is created when you:
•
Select a volume on the primary storage system that you want to copy.
•
Create or identify the volume on the secondary system that will contain the copy.
•
Connect the primary and secondary storage systems with a Fibre Channel channel data path.
•
Copy all primary system data to the secondary 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 split, writes to the P-VOL continue but are no longer copied to the S-VOL, and the
pair is no longer synchronized.
•
If a special S-VOL write option is enabled, the S-VOL becomes available for write access by
secondary hosts. If not enabled, the S-VOL remains unchanged from the time of the split.
•
Changes to P-VOL and S-VOL (if applicable) are tracked by differential bitmaps until the pair
is resynchronized.
•
When resynchronization takes place, only the changed data is transferred, reducing copy
time.
The XP7 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 Continuous Access Synchronous Z operations and other storage system processing are
performed at the same time, performance is affected.
To plan and implement a Continuous Access Synchronous Z system an understanding of its
components is required. This is provided in the following sections.
8 Continuous Access Synchronous Z overview