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Instant snapshots of ISP application volumes in a disk group's data pool are best created in clone pools that are also associated with the same disk group. A snapshot of a snapshot does not have to be in the same clone pool as its parent.
Volume sets can be used in place of volumes with the following vxsnap operations on instant snapshots: addmir, dis, make, prepare, reattach, refresh, restore, rmmir, split, syncpause, syncresume, syncstart, syncstop, syncwait, and unprepare.
A snapshot of a volume set must itself be a volume set. A full-sized instant snapshot of a volume set can be created using a prepared volume set. You cannot use the nmirrors or plex attributes to specify that existing plexes are to be broken off. See the section "Creating and Administering Volume Sets" in the Veritas Volume Manager Administrator's Guide for more information on creating volume sets.
VxVM allows you to make instant snapshots of volumes by using the vxsnap command.
A plex in a full-sized instant snapshot requires as much space as the original volume. If you instead make a space-optimized instant snapshot of a volume, this only requires enough storage to record the original contents of the parent volume as they are changed during the life of the snapshot.
The recommended approach to performing volume backup from the command line, or from a script, is to use the vxsnap command. The vxsnap prepare and make tasks allow you to back up volumes online with minimal disruption to users.
The vxsnap prepare step creates a DCO and DCO volume and associates this with the volume. It also enables Persistent FastResync on the volume.
The vxsnap make step creates an instant snapshot that is immediately available for making a backup. After the snapshot has been taken, read requests for data in the original volume are satisfied by reading either from a non-updated region of the original volume, or from the copy of the original contents of an updated region that have been recorded by the snapshot.
Synchronization of a full-sized instant snapshot from the original volume is enabled by default. If you specify the syncing=no attribute to vxsnap make, this disables synchronization, and the contents of the instant snapshot are unlikely ever to become fully synchronized with the contents of the original volume at the point in time that the snapshot was taken. If you wish to move an instant snapshot volume to another disk group for export to another machine for off-host processing, or to turn it into an independent volume, you must ensure that the snapshot volume has been completely synchronized.
You can immediately retake a full-sized, space-optimized or linked break-off snapshot at any time by using the vxsnap refresh command. If a fully synchronized full-sized or linked break-off snapshot is required, you must wait for the new resynchronization to complete.
To create and manage a snapshot of a volume with the vxsnap command, first follow the procedure to prepare for instant and break-off snapshots.
See Preparing to create instant and break-off snapshots.
Then use one of the procedures described in the following sections: