HP StorageWorks XP Remote Web Console Software - Manual (Page 118)

Table 29 Optimizing XP Continuous Access Operations and Storage System Performance
Recommendation(s) Description Condition
Spread write-intensive data across several
volumes to minimize queuing. Write-intensive workloads, such as
database logging volumes, can have a
significant impact on storage system I/O
response times. Write-intensive
workloads
Spread workloads with large write block
sizes across several volumes. Workloads with large write block sizes,
such as DB deferred writes, can impact
performance. Large block size
Spread the workload across several storage
systems to use additional channels. The demand on the MCU’s host channels
can affect performance. High host
channel demand
Avoid performing restore operations to
volumes which belong to XP Continuous
Access pairs. Instead, restore data to a
scratch volume, and then create the XP
Continuous Access pair. XP Continuous Access 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). Sequential write
operations
Consider increasing the cache size of the
XP Continuous Access storage systems to
handle sidefile operations and to improve
overall storage system performance. For
best results, the cache and NVS capacity
of the primary and secondary storage
systems should be the same (the RCU
sidefile requirements for XP Continuous
Access Asynchronous are twice that of the
MCU) to enable the remote site to function
adequately during disaster recovery. A large cache size improves read hit
performance, which allows more storage
system resources to be devoted to write
operations. The resulting performance
improvement can offset some or all of the
performance loss due to the XP Continuous
Access remote copy operations. XP
Continuous Access Asynchronous
(Compatible XRC, and Concurrent Copy)
requires additional cache for sidefile data.
Insufficient cache resources can result in
command retries, state-change-pending
(SCP) notifications, and puncture conditions. Cache size
Distribute XP Continuous Access remote
copy operations among several remote
storage systems to avoid overloading any
one RCU. The performance of the RCUs directly affects
the performance of the MCUs. If an RCU
becomes overloaded with heavy update
activity, MCU and system performance can
also be degraded. RCU capacity
Make sure to install an adequate number
of paths between the primary and
secondary storage systems. This is
especially important for storage systems
which contain both P-VOLs and S-VOLs. An inadequate number of paths may
decrease storage system performance.
Performing XP Continuous Access
Synchronous operations over long distances
can also degrade performance. XP
Continuous Access Asynchronous is
recommended for long distances. Paths
Discontinuing XP Continuous Access Operations
If you plan to use XP Continuous Access for nondisruptive data migration or duplication (see “Data
Migration Using XP Continuous Access Synchronous” (page 147) or “Point-in-Time (PiT) Data
Duplication Using XP Continuous Access Asynchronous” (page 148) ), you will configure and establish
XP Continuous Access operations, allow XP Continuous Access to synchronize the volumes, redirect
application I/Os (if migrating), and then discontinue XP Continuous Access operations. When you
are ready to discontinue XP Continuous Access operations, perform XP Continuous Access operations
in the correct order to avoid generating error messages. For example, XP Continuous Access will
not allow you to delete an RCU path until you have released all XP Continuous Access pairs still
using that path, and you cannot delete a group until you have released all XP Continuous Access
Asynchronous pairs in that group.
To discontinue all XP Continuous Access operations, perform the following actions:
1. Release all XP Continuous Access pairs from the MCU(s) (pairsplit-S, see “Releasing XP
Continuous Access Pairs” (page 140) ). For XP Continuous Access Asynchronous pairs, you can
118 Performing XP Continuous Access Configuration Operations