Controlling instant snapshot synchronization
Synchronization of the contents of a snapshot with its original volume is not possible for space-optimized instant snapshots.
By default, synchronization is enabled for the vxsnap reattach, refresh and restore operations on instant snapshots. Otherwise, synchronization is disabled unless you specify the syncing=yes attribute to the vxsnap command.
Commands for controlling instant snapshot synchronization shows the commands that are provided for controlling the synchronization manually.
Commands for controlling instant snapshot synchronization
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Command
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Description
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vxsnap [-g diskgroup] syncpause vol|vol_set
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Pause synchronization of a volume.
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vxsnap [-g diskgroup] syncresume \
vol|vol_set
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Resume synchronization of a volume.
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vxsnap [-b] [-g diskgroup] syncstart \
vol|vol_set
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Start synchronization of a volume. The -b option puts the operation in the background.
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vxsnap [-g diskgroup] syncstop vol|vol_set
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Stop synchronization of a volume.
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vxsnap [-g diskgroup] syncwait vol|vol_set
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Exit when synchronization of a volume is complete. An error is returned if vol is invalid (for example, it is a space-optimized snapshot), or if vol is not being synchronized.
Note
You cannot use this command to wait for synchronization of reattached plexes to complete.
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The commands that are shown in Commands for controlling instant snapshot synchronization cannot be used to control the synchronization of linked break-off snapshots.
The vxsnap snapwait command is provided to wait for the link between new linked break-off snapshots to become ACTIVE, or for reattached snapshot plexes to reach the SNAPDONE state following resynchronization.
See "Creating and managing linked break-off snapshot volumes" on page 339.
See "Reattaching an instant snapshot" on page 345.
See "Reattaching a linked break-off snapshot volume" on page 346.
Improving the performance of snapshot synchronization
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
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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.
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slow=iodelay
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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.
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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.
