HP StorageWorks XP Remote Web Console Software - Manual (Page 113)

Figure 46 CU Option Dialog Box
Maximum Initial Copy Activities: Allows you to specify the number of volumes on which copy
operations can be performed at the same time, from 1 to 16 volumes, for the selected CU.
Even if you set a value larger than the setting for Maximum Initial Copy Activities on the System
Option dialog box, the priority is given to Maximum Initial Copy Activities on the System Option
dialog box.
Optimizing XP Continuous Access Operations and Storage System
Performance
XP Continuous Access operations result in increased utilization of the storage system’s channel
resources because of the additional write (remote copy) operations to the secondary volumes. The
XP Continuous Access update copy mode (synchronous or asynchronous) determines exactly how
the remote copy operations will impact storage system performance as follows:
•
Synchronous copy mode has an additional effect on storage system performance: increased
service and disconnect time for write I/Os to XP Continuous Access P-VOLs due to the delay
between the channel-end and device-end. The length of this delay increases as the distance
between the P-VOL and S-VOL increases, so that the longest delay occurs when the primary
and secondary volumes are the maximum distance apart.
•
Asynchronous copy mode does not cause any delays which occur during the XP Continuous
Access Synchronous operation due to the distance between the P-VOL and S-VOL. However,
the response to the host is delayed compared to volumes that are not allocated to the XP
Continuous Access pair because additional processing time is required to create sidefile entries
for the asynchronous copy.
The only performance concerns for XP Continuous Access Asynchronous are (1) ensuring that
adequate cache resources are available for sidefiles that are used to store the recordsets at
both the MCUs and RCUs, and (2) ensuring that sufficient MCU-RCU paths are defined for
copy operations.
In addition to the XP Continuous Access update copy mode, several other factors can also affect
storage system performance. You can optimize both the XP Continuous Access operations and the
I/O performance of the storage systems by analyzing workloads and addressing system-level
conditions (for example, number of host-interface paths) that can affect storage system performance.
You can also control the impact of XP Continuous Access operations on storage system performance
by selecting the appropriate RCU options for each MCU and the appropriate update copy mode
(synchronous or asynchronous), initial copy options, and pair options for each XP Continuous
Access pair. In addition, you can upgrade the XP Continuous Access hardware components and/or
adjust the configuration of the components to improve storage system performance under a wide
range of operating conditions.
For important information about proper configuration for your operational environment, see “XP
Continuous Access Load Balancing and Sidefile Management and Control” (page 169) .
Table 29 (page 114) lists some of the conditions that affect storage system performance and provides
recommendations for addressing these conditions.
Optimizing XP Continuous Access Operations and Storage System Performance 113