HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)

Figure 41 CU Op
tion Dialog Box
• Maximum Initial Copy Activities: Allows you to specif y 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 se
t a
value larger than the setting for Maximum Initial Copy Activities on the System
Option dialog box, the priority i s given to Maximum Initial C opy Activities on the System Option
dialog box.
Optimizing Continuous Access Operations and Storage
System Performance
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 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 Continuous Access P-VOLs due to the d elay between
the
channel-end and d evice-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 apar t.
• Asynchronous copy mode eliminates all delays associated with Continuous Access Synchronous
operations while providing increased protection for write-dependent applications in the event
of a
disaster. Write I/O s for Continuous Access Asynchronous P-VOLs are processed in the
same
way as writes for simplex volumes, without any increase in service or disconnect time.
The asynchronous S-VOL updates are performed completely independent of all host I/O
processes a t the P-VOLs, and there are no restrictions on subsequent read/write op erations to
Continuous Access Asynchronous P-VOLs. The only performance concerns for Continuous Access
Asynchronous are (1) ensuring that ad equate cache resourc es are available for sidefiles which
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 Continuous Access update copy mode, several other factors can also affect storage
system performance. You can o ptim ize both the Continuous Access operations and the I/O p erformance
of the
storage systems by ana lyzing workloads and addressing system-level conditions (for example,
number of host interface pa ths) which can affect storage system performance. You can also control the
impact of Continuous Access operations on storage system per formance by selecting the appropriate RCU
options for ea ch MCU ( see “Changing the RCU Options” on page 75) and the appropriate update copy
mode (synchronous or asynchronous), initial copy options ( see “Initial Copy Options” on page 109), and
pair options (see “ Pair Options” on page 110) for each Continuous Access pair. In addition, you can
upgrade the Continuous Access hardware components and/or adjust the con figuration of the components
to
improve storage system performance u nder a wide range of operating conditions.
Note: For important information about proper configuration for your operational environment, see
“Continuous Access Load Balancing and Sidefile Management and Control” on page 143.
Table 21 on page 97 lists some of the conditions which affect storage system per formance and provides
recommendations for addressing these conditions.
96
Performing Continuous Access Configuration Operations