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345Administering volume snapshots
Creating instant snapshots
instant snapshot” on page 338 and “Reattaching a linked break-off snapshot
volume” on page 339 for details.
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.
Listing the snapshots created on a cache
To list the space-optimized instant snapshots that have been created on a cache
object, use the following command:
# vxcache [-g diskgroup] listvol cache_object
The snapshot names are printed as a space-separated list ordered by timestamp.
If two or more snapshots have the same timestamp, these snapshots are sorted
in order of decreasing size.