Veritas Storage Foundation Intelligent Storage Provisioning 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

119Administering instant snapshots
Creating instant snapshots
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.