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Implementing off-host online backup

This section describes a procedure for implementing off-host online backup for a volume in a private disk group. The intention is to present an outline of how to set up a regular backup cycle. It is beyond the scope of this guide to describe how to configure a database to use this procedure, or how to perform the backup itself.

 To back up a volume in a private disk group

1. Use the following command on the primary host to see if the volume is associated with a version 20 data change object (DCO) and DCO volume that allow instant snapshots and Persistent FastResync to be used with the volume:

   # vxprint -g volumedg -F%instant volume

   This command returns on if the volume can be used for instant snapshot operations; otherwise, it returns off.

2. Use the following command on the primary host to check whether FastResync is enabled on the volume:

   # vxprint -g volumedg -F%fastresync volume

   This command returns on if FastResync is enabled; otherwise, it returns off.

   If FastResync is disabled, enable it using the following command on the primary host:

   # vxvol -g volumedg set fastresync=on volume

3. On the primary host, create a new volume in a separate disk group for use as the snapshot volume.

   See "Creating a volume for use as a full-sized instant or linked break-off snapshot" on page 305.

   It is recommended that a snapshot disk group is dedicated to maintaining only those disks that are used for off-host processing.

4. On the primary host, link the snapshot volume in the snapshot disk group to the data volume:

   # vxsnap -g volumedg -b addmir volume mirvol=snapvol \

     mirdg=snapvoldg

   You can use the vxsnap snapwait command to wait for synchronization of the linked snapshot volume to complete:

   # vxsnap -g volumedg snapwait volume mirvol=snapvol \

     mirdg=snapvoldg

This step sets up the snapshot volumes, and starts tracking changes to the original volumes.

When you are ready to create a backup, proceed to step 5.

5. On the primary host, suspend updates to the volume that contains the database tables. A database may have a hot backup mode that allows you to do this by temporarily suspending writes to its tables.
6. Create the snapshot volume, snapvol, by running the following command on the primary host:

   # vxsnap -g volumedg make \

     source=volume/snapvol=snapvol/snapdg=snapvoldg

   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/snapvol=snapvol1/snapdg=sdg \

     source=vol2/snapvol=snapvol2/snapdg=sdg \

     source=vol3/snapvol=snapvol3/snapdg=sdg

7. On the primary host, if you temporarily suspended updates to a volume in step 5, release all the database tables from hot backup mode.
8. On the primary host, deport the snapshot volume's disk group using the following command:

   # vxdg deport snapvoldg

9. On the OHP host where the backup is to be performed, use the following command to import the snapshot volume's disk group:

   # vxdg import snapvoldg

10. The snapshot volume is initially disabled following the join. Use the following commands on the OHP host to recover and restart the snapshot volume:

    # vxrecover -g snapvoldg -m snapvol

    # vxvol -g snapvoldg start snapvol

11. On the OHP host, back up the snapshot volume. If you need to remount the file system in the volume to back it up, first run fsck on the volume. The following are sample commands for checking and mounting a file system:

    # fsck -V vxfs /dev/vx/dsk/snapvoldg/snapvol

    # mount -V vxfs /dev/vx/dsk/snapvoldg/snapvol mount_point

    Back up the file system at this point, and then use the following command to unmount it.

    # umount mount_point

12. On the OHP host, use the following command to deport the snapshot volume's disk group:

    # vxdg deport snapvoldg

13. On the primary host, re-import the snapshot volume's disk group using the following command:

    # vxdg import snapvoldg

14. The snapshot volume is initially disabled following the join. Use the following commands on the primary host to recover and restart the snapshot volume:

    # vxrecover -g snapvoldg -m snapvol

    # vxvol -g snapvoldg start snapvol

15. On the primary host, reattach the snapshot volume to its original volume using the following command:

    # vxsnap -g snapvoldg reattach snapvol source=vol \

      sourcedg=volumedg

    For example, to reattach the snapshot volumes svol1, svol2 and svol3:

    # vxsnap -g sdg reattach svol1 \

      source=vol1 sourcedg=dbasedg \

      svol2 source=vol2 sourcedg=dbasedg \

      svol3 source=vol3 sourcedg=dbasedg

    You can use the vxsnap snapwait command to wait for synchronization of the linked snapshot volume to complete:

    # vxsnap -g volumedg snapwait volume mirvol=snapvol

    Repeat step 5 through step 15 each time that you need to back up the volume.