InfoScale™ 9.0 Solutions Guide - Linux

To prepare to back up a snapshot of a mounted file system which has shared access

1. On the master node, verify that the volume has an instant snap data change object (DCO) and DCO volume, and that FastResync is enabled on the volume:

   # vxprint -g database_dg -F%instant database_vol

   # vxprint -g database_dg -F%fastresync database_vol

   If both commands return the value of ON, proceed to step 3. Otherwise, continue with step 2.

2. Use the following command to prepare a volume for instant snapshots:

   # vxsnap -g database_dg prepare database_vol [regionsize=size] \ 
   [ndcomirs=number] [alloc=storage_attributes]

3. Use the vxprint command on the original volume to find the required size for the snapshot volume.

   # LEN=`vxprint [-g database_dg] -F%len database_vol`

   Note:

   The command shown in this and subsequent steps assumes that you are using a Bourne-type shell such as sh, ksh or bash. You may need to modify the command for other shells such as csh or tcsh. These steps are valid only for instant snap DCOs.

4. Use the vxprint command on the original volume to discover the name of its DCO:

   #  DCONAME=`vxprint [-g database_dg] -F%dco_name database_vol`

5. Use the vxprint command on the DCO to discover its region size (in blocks):

   # RSZ=`vxprint [-g database_dg] -F%regionsz $DCONAME`

6. Use the vxassist command to create a volume, snapvol, of the required size and redundancy, together with an instant snap DCO volume with the correct region size:

   # vxassist [-g database_dg] make snapvol $LEN \
     [layout=mirror nmirror=number] logtype=dco drl=no \
     dcoversion=20 [ndcomirror=number] regionsz=$RSZ \
     init=active [storage_attributes]

   It is recommended that you specify the same number of DCO mirrors (ndcomirror) as the number of mirrors in the volume (nmirror). The init=active attribute is used to make the volume available immediately. You can use storage attributes to specify which disks should be used for the volume.

   As an alternative to creating the snapshot volume and its DCO volume in a single step, you can first create the volume, and then prepare it for instant snapshot operations as shown here:

   # vxassist [-g database_dg] make snapvol $LEN \
     [layout=mirror nmirror=number] init=active \
     [storage_attributes]
   # vxsnap [-g database_dg] prepare snapvol [ndcomirs=number] \
     regionsz=$RSZ [storage_attributes]

7. Then use the following command to create the snapshot:

   # vxsnap -g database_dg make source=database_dg/snapvol=snapvol

   Note:

   This step actually takes the snapshot and sets up the snapshot volumes ready for the backup cycle, and starts tracking changes to the original volumes.