Third-mirror break-off snapshots are suitable for write-intensive volumes (such as for database redo logs) where the copy-on-write mechanism of space-optimized or full-sized instant snapshots might degrade the performance of the volume.
If you use the vxsnap
prepare
command to enable a volume for use with instant and space-optimized snapshots, you cannot use the vxassist
snapshot commands to administer snapshots that you create for the volume. If you require snapshots that behave as third-mirror break-off snapshots (that is, they must be fully synchronized before they can be used), there are three ways to achieve this:
vxsnap
addmir
command to create and attach one or more snapshot mirrors to the volume. When the plexes have been synchronized and are in the SNAPDONE
state, the vxsnap
make
command can then be used with the nmirror
attribute to create the snapshot volume. This technique is similar to using the vxassist
snapstart
and vxassist
snapshot
commands.
See "Traditional third-mirror break-off snapshots" on page 313.
vxsnap
make
command with the plex
attribute to use one or more existing plexes of a volume as snapshot plexes. The volume must have a sufficient number of available plexes that are in the ACTIVE
state.
The volume must be a non-layered volume with a mirror
or mirror-stripe
layout, or a RAID-5 volume that you have converted to a special layered volume and then mirrored.
See "Using a DCO and DCO volume with a RAID-5 volume" on page 286.
The plexes in a volume with a stripe-mirror
layout are mirrored at the sub-volume level, and cannot be broken off.
vxsnap
make
command with the sync=yes
and type=full
attributes specified to create the snapshot volume, and then use the vxsnap
syncwait
command to wait for synchronization of the snapshot volume to complete.
See "Adding snapshot mirrors to a volume" on page 341.
See "Creating and managing third-mirror break-off snapshots" on page 334.