Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

5-60 Performing TrueCopy for z/OS Configuration Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Configuring and Maintaining Your TCz Environment
Optimizing TrueCopy for z/OS Operations and Storage System
Performance
All TCz operations result in increased utilization of the USP V’s channel
resources because of the additional write (remote copy) operations to the
secondary volumes. The TCz update copy mode (synchronous or
asynchronous) determines exactly how the remote copy operations will impact
storage system performance as follows:
• Synchronous copy mode (TCz Synchronous) has an additional effect on
storage system performance: increased service and disconnect time for write
I/Os to TCz M-VOLs due to the delay between channel-end and device-end.
The length of this delay increases as the distance between the M-VOL and R-
VOL increases, so that the longest delay occurs when the main and remote
volumes are the maximum distance apart.
• Asynchronous copy mode (TCzA) eliminates all delays associated with TCz
Synchronous operations while providing increased protections for write-
dependent applications in the event of a disaster. Write I/Os for TCzA M-VOLs
are processed in the same way as writes for simplex volumes, without any
increase in service or disconnect time. The asynchronous R-VOL updates are
performed completely independent of all host I/O processes at the M-VOLs,
and there are no restrictions on subsequent read/write operations to TCzA M-
VOLs. The only performance concerns for TCzA are:
– To ensure that adequate cache resources are available for sidefiles which
are used to store the recordsets at both the MCUs and RCUs.
– To ensure that sufficient MCU-RCU paths are defined for copy operations.
In addition to the TCz update copy mode, several other factors can also affect
USP V performance. You can optimize both the TCz operations and the I/O
performance of the storage systems by analyzing workloads and addressing
system-level conditions (e.g., number of remote copy connection paths) which
can affect storage system performance.
You can also control the impact of TCz operations on storage system
performance by selecting the appropriate RCU options for each MCU and the
appropriate update copy mode (synchronous or asynchronous) and pair
options for each TCz pair. In addition, you can upgrade the TCz hardware
components and/or adjust the configuration of the components to improve
storage system performance under a wide range of operating conditions.
Table 5-7 lists some of the conditions which affect storage system
performance and provides recommendations for addressing these conditions.