InfoScale™ 9.0 Solutions Guide - AIX

To prepare a space-optimized snapshot for a backup of an online database

1. Decide on the following characteristics that you want to allocate to the cache volume that underlies the cache object:

   • The size of the cache volume should be sufficient to record changes to the parent volumes during the interval between snapshot refreshes. A suggested value is 10% of the total size of the parent volumes for a refresh interval of 24 hours.

   • If redundancy is a desired characteristic of the cache volume, it should be mirrored. This increases the space that is required for the cache volume in proportion to the number of mirrors that it has.

   • If the cache volume is mirrored, space is required on at least as many disks as it has mirrors. These disks should not be shared with the disks used for the parent volumes. The disks should also be chosen to avoid impacting I/O performance for critical volumes, or hindering disk group split and join operations.

2. Having decided on its characteristics, use the vxassist command to create the volume that is to be used for the cache volume. The following example creates a mirrored cache volume, cachevol, with size 1GB in the disk group, database_dg, on the disks disk16 and disk17:

   # vxassist -g database_dg make cachevol 1g layout=mirror \
     init=active disk16 disk17

   The attribute init=active is specified to make the cache volume immediately available for use.

3. Use the vxmake cache command to create a cache object on top of the cache volume that you created in the previous step:

   #  vxmake [-g diskgroup] cache cache_object \
     cachevolname=cachevol [regionsize=size] [autogrow=on] \
     [highwatermark=hwmk] [autogrowby=agbvalue] \
     [maxautogrow=maxagbvalue]]

   If you specify the region size, it must be a power of 2, and be greater than or equal to 16KB (16k). If not specified, the region size of the cache is set to 64KB.

   Note:

   All space-optimized snapshots that share the cache must have a region size that is equal to or an integer multiple of the region size set on the cache. Snapshot creation also fails if the original volume's region size is smaller than the cache's region size.

   If the cache is not allowed to grow in size as required, specify autogrow=off. By default, the ability to automatically grow the cache is turned on.

   In the following example, the cache object, cache_object, is created over the cache volume, cachevol, the region size of the cache is set to 32KB, and the autogrow feature is enabled:

   # vxmake -g database_dg cache cache_object cachevolname=cachevol \
     regionsize=32k autogrow=on

4. Having created the cache object, use the following command to enable it:

   vxcache [-g diskgroup] start cache_object

   For example, start the cache object cache_object:

   # vxcache -g database_dg start cache_object

5. Create a space-optimized snapshot with your cache object.

   # vxsnap -g database_dg make \
   source=database_vol1/newvol=snapvol1/cache=cache_object
   

6. If several space-optimized snapshots are to be created at the same time, these can all specify the same cache object as shown in this example:

   # vxsnap -g database_dg make \
     source=database_vol1/newvol=snapvol1/cache=cache_object \
     source=database_vol2/newvol=snapvol2/cache=cache_object \
     source=database_vol3/newvol=snapvol3/cache=cache_object

   Note:

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

   When you are ready to make a backup, proceed to make a backup of an online database on the same host