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351Administering volume snapshots
Creating traditional third-mirror break-off snapshots
Note: Dissociating or removing the snapshot volume loses the advantage of
fast resynchronization if FastResync was enabled. If there are no further
snapshot plexes available, any subsequent snapshots that you take require
another complete copy of the original volume to be made.
Converting a plex into a snapshot plex
Note: The procedure described in this section cannot be used with layered
volumes or any volume that has an associated version 20 DCO volume.
It is recommended that the instant snapshot feature is used in preference to the
procedure described in this section.
In some circumstances, you may find it more convenient to convert an existing
plex in a volume into a snapshot plex rather than running vxassist snapstart.
For example, you may want to do this if you are short of disk space for creating
the snapshot plex and the volume that you want to snapshot contains more than
two plexes.
The procedure can also be used to speed up the creation of a snapshot volume
when a mirrored volume is created with more than two plexes and
init=active
is specified.
Note: It is advisable to retain at least two plexes in a volume to maintain data
redundancy.
To convert an existing plex into a snapshot plex for a volume on which
Persistent FastResync is enabled, use the following command:
# vxplex [-g diskgroup] -o dcoplex=dcologplex convert \
state=SNAPDONE plex
dcologplex is the name of an existing DCO plex that is to be associated with the
new snapshot plex. You can use the
vxprint command to find out the name of
the DCO volume as described in “Adding a version 0 DCO and DCO volume” on
page 356.
For example, to make a snapshot plex from the plex trivol-03 in the 3-plex
volume trivol, you would use the following command:
# vxplex -o dcoplex=trivol_dco-03 convert state=SNAPDONE \
trivol-03
Here the DCO plex trivol_dco_03 is specified as the DCO plex for the new
snapshot plex.