Administering volume snapshots 311

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-mirrorbreak-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.
ATTACHINGSynchronization 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.
BROKENThe 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