HP XP P9500 Storage - Manual (Page 7)

1 Continuous Access Synchronous Z overview
Unless otherwise specified, the term P9000 in this guide refers to the following disk array:
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P9500 Disk Array
The GUI illustrations in this guide were created using a Windows computer with the Internet Explorer
browser. Actual windows may differ depending on the operating system and browser used. GUI
contents also vary with licensed program products, storage system models, and firmware versions.
Continuous Access Synchronous Z helps you create and maintain a synchronous backup of critical
data in a remote location. This manual provides information and instructions for planning,
configuring, creating, maintaining, monitoring, and troubleshooting a Continuous Access
Synchronous Z synchronous system on P9500 storage systems.
A Continuous Access Synchronous Z system creates and maintains a mirror image of a production
volume at a remote location. Data in a remote disk array using Continuous Access Synchronous
Z stays synchronized with the data in the local P9500 system. This happens when data is written
from the host to the local disk array then to the remote disk array through an interconnecting Fibre
Channel data path. The local disk array acknowledges the write I/O operation is complete to the
host after the remote disk array has acknowledged to the local disk array that the copy data has
been received.
Continuous Access Synchronous Z can be teamed with Business Copy 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.
How Continuous Access Synchronous Z works
A pair is created in the following procedure:
1. Select a volume on the local system that you want to copy.
2. Create or identify the volume on the remote system that will contain the copy.
3. Connect the local and remote systems with a Fibre Channel data path
4. Copy all local volume data to the remote volume.
During a typical initial copy, all data written to the local volume (M-VOL) is copied to the remote
volume (R-VOL), insuring that the secondary copy is a complete and consistent backup.
When a pair is suspended, writes to the local volume continues but are no longer copied to the
secondary side, and the pair is no longer synchronous.
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If a special R-VOL write option is enabled, the remote volume becomes available for read/write
access by secondary host applications. Otherwise the R-VOL remains as it was at the time of
the suspension.
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Changes to local and remote volumes (if applicable) are tracked by differential bitmaps until
the local and remote volumes are resynchronized.
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When resynchronization takes place, only the changed data is transferred, reducing copy
time.
Continuous Access Synchronous Z 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 is used, the copy processing of Continuous Access
Synchronous Z is performed in addition to the processing to the volume not allocated to the
Continuous Access Synchronous Z pair. Therefore, there is a possibility that the performance
decreases compared with the case where Continuous Access Synchronous Z is not used and rises
utilization rates.
How Continuous Access Synchronous Z works 7