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311Administering volume snapshots
Linked break-off snapshot volumes
■ Use the 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 “Creating and managing third-mirror break-off snapshots” on page 329 for
details of the procedures for creating and using this type of snapshot.
For information about how to add snapshot mirrors to a volume, see “Adding
snapshot mirrors to a volume” on page 336.
Linked break-off snapshot volumes
A variant of the third-mirror break-off snapshot type are linked break-off
snapshot volumes, which use the
vxsnap addmir command to link a specially
prepared volume with the data volume. The volume that is used for the snapshot
is prepared in the same way as for full-sized instant snapshots. However, unlike
full-sized instant snapshots, this volume can be set up in a different disk group
from the data volume. This makes linked break-off snapshots especially suitable
for off-host processing applications where you may want to create the snapshot
on storage with different characteristics from that used for the data volumes. As
for third-mirror break-off snapshots, you must wait for the contents of the
snapshot volume to be synchronized with the data volume before you can use
the
vxsnap make command to take the snapshot.
When a link is created between a volume and the mirror that will become the
snapshot, separate link objects (similar to snap objects) are associated with the
volume and with its mirror. The link object for the original volume points to the
mirror volume, and the link object for the mirror volume points to the original
volume. All I/O is directed to both the original volume and its mirror, and a
synchronization of the mirror from the data in the original volume is started.
You can use the
vxprint command to display the state of link objects, which
appear as type ln. Link objects can have the following states:
ACTIVE The mirror volume has been fully synchronized from the
original volume. The
vxsnap make command can be run to
create a snapshot volume.
ATTACHING Synchronization of the mirror volume is in progress. The
vxsnap make command cannot be used to create a snapshot
volume until the state changes to ACTIVE. The
vxsnap
snapwait command can be used to wait for the
synchronization to complete.
BROKEN The mirror volume has been detached from the original
volume because of an I/O error or an unsuccessful attempt to
grow the mirror volume. The
vxrecover command can be used