9.4.1 Sizing Steps for New Sparse Disk Groups

These steps describe how to determine the space needed for sparse disk groups and how to allocate that space.

The maximum physical size that can be allocated to sparse grid disks from a single cell disk is 4 TB.

The maximum virtual size that can be allocated per sparse grid disk is 100 TB. However, to avoid additional performance impact Oracle does not recommend creating large virtual sizes unless it is truly required.

Remember also that a sparse disk group can house non-sparse database files, in which case the physical storage utilization matches the virtual file size.

1. Determine the amount of physical space for your snapshots. Use the formula found in Calculating the Physical Size for Grid Disks.

   Note that a good maximum starting point for physical space allocation for sparse grid disk is 15% of your total space. This can be tuned up or down as required based on utilization patterns and future needs.

2. Determine the amount of virtual space you will require for your snapshots. Use the formula found in Calculating the Virtual Size for Grid Disks.

   Note that the virtual size can be modified online by modifying the Oracle ASM disk group without making any changes to the underlying grid disks.

3. Using the number of snapshots you plan on having at any one time and how much changes you expect to make, use the process defined in Determine the Amount of Available Space to determine which existing disk group(s) you want to shrink to release space for the sparse disk group. Based on your current allocations, you may need to shrink multiple disk groups to get the space you require for the sparse disk group. Leave a minimum of 15% free space in the original disk groups to allow for rebalancing during the resize operation.

   If there is not enough free space available in your current disk groups to provide desired space for the sparse disk group:

   • Rethink your sparse usage in this environment and downsize accordingly
   • Relocate objects and databases from this environment to another with available free space
   • Add storage
4. Once you have decided which disk group to resize, follow the steps in Shrink the Oracle ASM Disks in the Donor Disk Group and Shrink the Grid Disks in the Donor Disk Group to resize the disks.

   This process allows you to resize disks while they are online and only require a single rebalance operation per disk group. Oracle ASM may run more than one rebalance operation concurrently, depending on the number of Oracle ASM instances available in the cluster.

5. Create the sparse grid disk from the space just released using the commands outlined in Creating Sparse Grid Disks.
6. Create the sparse Oracle ASM disk group using the commands outlined in Resizing the Physical Space.
7. To monitor sparse grid disk activity see Monitoring Sparse Disk Group Utilization.
8. If you find that you need to resize your sparse grid disks:

   • If more physical space is required, follow steps 1 through 4 in this section to free up space and then follow the steps in Resizing the Physical Space. The maximum physical size that can be allocated to sparse grid disks from a single cell disk is 4 TB.

   • If more virtual space is required, follow the steps in Resizing the Virtual Space. The maximum virtual size that can be allocated to sparse grid disks from a single cell disk is 100 TB.