Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Implementing Off-Host Processing Solutions
324 VERITAS Volume Manager Administrator’s Guide
If you created a new volume, snapvol, for use as the snapshot volume in step 4, use the
following version of the vxsnap command to create the snapshot on this volume:
# vxsnap -g volumedg make source=volume/snapvol=snapvol
Note By default, VxVM attempts to avoid placing snapshot mirrors on a disk that
already holds any plexes of a data volume. However, this may be impossible if
insufficient space is available in the disk group. In this case, VxVM uses any
available space on other disks in the disk group. If the snapshot plexes are
placed on disks which are used to hold the plexes of other volumes, this may
cause problems when you subsequently attempt to move a snapshot volume
into another disk group as described in “Moving DCO Volumes Between Disk
Groups” on page 161. To override the default storage allocation policy, you can
use storage attributes to specify explicitly which disks to use for the snapshot
plexes. See “Creating a Volume on Specific Disks” on page 203 for more
information.
If a database spans more than one volume, you can specify all the volumes and their
snapshot volumes using one command, as shown in this example:
# vxsnap -g dbasedg make source=vol1/newvol=snapvol1/nmirror=2 \
source=vol2/newvol=snapvol2/nmirror=2 \
source=vol3/newvol=snapvol3/nmirror=2
Note This step sets up the snapshot volumes, and starts tracking changes to the
original volumes. When you are ready to create a replica database, proceed to
step 6.
6. On the primary host, suspend updates to the volume that contains the database
tables. The database may have a hot backup mode that allows you to do this by
temporarily suspending writes to its tables.
7. On the primary host, refresh the plexes of the snapshot volume using the following
command:
# vxsnap [-g diskgroup] refresh snapvol source=volume syncing=yes
The syncing=yes attribute starts a synchronization of the snapshot in the
background.
For a database, multiple snapshots can be refreshed in parallel, as shown in this
example:
# vxsnap -g dbasedg refresh snapvol1 source=vol1 snapvol2 \
source=vol2 snapvol3 source=vol3 syncing=yes