Improving the performance of snapshot synchronization


Improving the performance of snapshot synchronization
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The following optional arguments to the -o option are provided to help optimize the performance of synchronization when using the make, refresh, restore and syncstart operations with full-sized instant snapshots:

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:

The iosize and slow parameters are not supported for space-optimized snapshots.