VERITAS Storage Foundation 4.1 Intelligent Storage Provisioning Administrator's Guide

Implementing Off-Host Processing Solutions
92 VERITAS Storage Foundation ISP Administrator’s Guide
Improving the Performance of Snapshot Synchronization
Two optional arguments to the -o option are provided to help optimize the performance of
synchronization when using the make, refresh, restore and syncstart operations:
iosize=size Specifies the size of each I/O request that is used when synchronizing the
regions of a volume. Specifying a larger size causes synchronization to
complete sooner, but with greater impact on the performance of other
processes that are accessing the volume. The default size of 1m (1MB) is
suggested as the minimum value for high-performance array and
controller hardware. The specified value is rounded to a multiple of the
volume’s region size.
slow=iodelay Specifies the delay in milliseconds between synchronizing successive sets
of regions as specified by the value of iosize. This can be used to
change the impact of synchronization on system performance. The default
value of iodelay is 0 milliseconds (no delay). Increasing this value slows
down synchronization, and reduces the competition for I/O bandwidth
with other processes that may be accessing the volume.
Options may be combined as shown in the following examples:
# vxsnap -g mydg -o iosize=2m,slow=100 make \
source=myvol/snapvol=snap2myvol/syncing=on
# vxsnap -g mydg -o iosize=10m,slow=250 syncstart snap2myvol
Note These optional parameters only affect the synchronization of full-sized instant snapshots.
They are not supported for space-optimized snapshots.
Implementing Off-Host Processing Solutions
By importing snapshot volumes on a lightly loaded host, CPU- and I/O-intensive operations for
online backup and decision support do not degrade the performance of the primary host that is
performing the main production activity (such as running a database). If the snapshot volumes are
configured on disks that are attached to different host controllers than the disks in the primary
volumes, it is possible to avoid contending with the primary host for I/O resources.
The following sections describe how you can apply off-host processing to implement regular online
backup of a volume in a private disk group, and to set up a replica of a production database for
decision support. Two applications are outlined in the following sections:
◆ Implementing Off-Host Online Backup
◆ Implementing Decision Support