HP XP Continuous Access Software - Manual (Page 76)

76 Continuous Access XP for the XP1024/XP128
• Stopping the usage monitoring function by clicking Stop in the Operation drop-down list, and clicking
Apply.
• Clicking another tab.
• Exiting Command View XP or XP Remote Web Console.
Optimizing Continuous Access XP operations and disk array performance
Continuous Access XP operations result in increased utilization of the disk array’s channel resources
because of additional write (remote copy) operations to secondary volumes. The Continuous Access XP
update copy mode (synchronous or asynchronous) determines exactly how the remote copy operations
impact disk array performance as follows:
• Synchronous copy mode has an additional effect on disk array performance: increased service and
disconnect time for write I/Os to Continuous Access XP P-VOLs due to the delay between channel-end
and device-end. The length of this delay increases as the distance between the P-VOL and S-VOL
increases, so the longest delay occurs when primary and secondary volumes are the maximum
distance apart.
• Asynchronous copy mode (Continuous Access XP Asynchronous) eliminates all delays associated with
Continuous Access XP Synchronous operations while providing protection for write-dependent
applications if a disaster occurs. Write I/Os for Continuous Access XP Async P-VOLs are processed
the same way as writes for simplex volumes, without any increase in service or disconnect time.
Asynchronous S-VOL updates are performed completely independent of all host I/O processes at
P-VOLs, and there are no restrictions on subsequent read and write operations to Continuous Access
XP Async P-VOLs. The only performance concerns for Continuous Access XP Asynchronous are:
• Ensuring adequate cache resources are available for sidefiles used to store recordsets at MCUs
and RCUs
• Ensuring sufficient Fibre Channel paths are defined for copy operations
In addition to Continuous Access XP update copy mode, several other factors can also affect disk array
performance. You can optimize Continuous Access XP operations and I/O performance of disk arrays by
analyzing workloads and addressing system-level conditions (for example, number of Fibre Channel
paths) that can affect disk array performance. You can also control the impact of Continuous Access XP
operations on disk array performance by selecting the appropriate RCU options for each MCU (see
” Registering RCUs (Add RCU) ” on page 56 and ” Modifying RCU options (Change RCU Option) ” on
page 60) and the appropriate update copy mode (synchronous or asynchronous) and pair options (see
” Creating Continuous Access XP volume pairs (Paircreate) ” on page 81) for each Continuous Access XP
pair. In addition, you can upgrade Continuous Access XP hardware components and adjust the
configuration of components to improve disk array performance under a wide range of operating
conditions.
Table 18 lists conditions affecting disk array performance and provides recommendations for addressing
these conditions.
Table 18 Disk array performance conditions and recommendations
Condition Description Recommendations
Write-intensive
workloads
Write-intensive workloads, such as database
logging volumes, can have a significant
impact on disk array I/O response times.
Spread write-intensive data across several
volumes to minimize queuing. Also consider
increasing the duplex write line (DWL) of the
disk array using Performance Advisor
(Performance Advisor running at the same
time is not supported).
Large block size Workloads with large write block sizes,
such as DB deferred writes, can impact
performance.
Spread workloads with large write block
sizes across several volumes.
High host channel
demand
Demand on MCU’s host channels can affect
performance.
Spread workloads across several disk arrays
to utilize additional channels.