Discontinuing Continuous Access Xp Operations; Disk Array Performance Conditions And Recommendations - HP StorageWorks XP12000 User Manual

Table 27 lists conditions affecting disk array performance and provides recommendations for addressing
these conditions.
Table 27 Disk array performance conditions and recommendations
Condition
Write-intensive
workloads
Large block size
High host channel
demand
Sequential write
operations
Cache size
RCU capacity
Paths

Discontinuing Continuous Access XP operations

If you plan to use Continuous Access XP for nondisruptive data migration or duplication configure and
establish Continuous Access XP operations, allow Continuous Access XP to synchronize volumes, redirect
application I/Os (if migrating), and discontinue Continuous Access XP operations. When you are ready
to discontinue Continuous Access XP operations, perform Continuous Access XP operations in the correct
order to avoid error messages. For example, Continuous Access XP will not delete an RCU path until
you delete all Continuous Access XP pairs still using that path, and you cannot delete a group until you
delete all Continuous Access XP Asynchronous pairs in that group.
98
Continuous Access XP for the Array
Description
Write-intensive workloads, such as
database logging volumes, can have
a significant impact on disk array I/O
response times.
Workloads with large write block sizes,
such as DB deferred writes, can impact
performance.
Demand on MCU's host channels can
affect performance.
Continuous Access XP operations can
have a negative impact on workloads
with a high percentage of sequential write
operations, such as batch processing
operations (for example, dump/restore,
sort operations).
Large cache size improves read hit
performance, which allows more disk
array resources to be devoted to write
operations. Resulting performance
improvements can offset some or all
performance losses due to Continuous
Access XP remote copy operations.
Continuous Access XP Asynchronous
requires additional cache for sidefile
data. Insufficient cache resources
can result in command retries,
state-change-pending (SCP) notifications,
and puncture conditions.
Performance of RCUs directly affects
performance of MCUs. If an RCU is
overloaded with heavy update activity,
MCU and system performance can also
be degraded.
An inadequate number of paths may
decrease disk array performance.
Performing Continuous Access XP
Synchronous operations over long
distances can also degrade performance.
Continuous Access XP Asynchronous is
recommended for long distances.
Recommendations
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 XP (Performance
Advisor XP running at the same time is
not supported).
Spread workloads with large write block
sizes across several volumes.
Spread workloads across several disk
arrays to utilize additional channels.
Avoid performing restore operations
to volumes belonging to Continuous
Access XP pairs. Instead, restore data
to a scratch volume and then create the
Continuous Access XP volume pair.
Consider increasing cache size of
Continuous Access XP disk arrays to
handle cache sidefile operations and
improve overall disk array performance.
For best results, cache and NVS capacity
of primary and secondary disk arrays
should be the same (for Continuous
Access XP Asynchronous, RCU sidefile
requirements are twice that of the MCU)
to enable the remote site to function
adequately during disaster recovery.
Distribute Continuous Access XP remote
copy operations among several remote
disk arrays to avoid overloading any one
RCU.
Ensure an adequate number of paths
between the primary and secondary disk
arrays are installed. This is especially
important for disk arrays containing both
P-VOLs and S-VOLs.