Exadata Snapshots utilize Oracle ASM sparse disk groups.

Sparse data files can be created only in Oracle Automatic Storage Management (Oracle ASM) sparse disk groups. The following figure shows a sparse disk group containing three Exadata Snapshots.

A sparse disk group has the following attributes:

• compatible.asm must be set to 12.1.0.2 or higher.
• compatible.rdbms must be set to 12.1.0.2 or higher.
• cell.smart_scan_capable must be set to true.
• cell.sparse_dg must be set to allsparse. This attribute identifies the disk group to Oracle ASM as being made up of sparse grid disks.
• As is the case for all Oracle ASM disk groups on Exadata, the recommended allocation unit (AU) size is 4M.

For example, the following SQL command creates a sparse disk group:

SQL> CREATE DISKGROUP SPARSE
  NORMAL REDUNDANCY 
  DISK 'o/*/SPARSE_*'
  ATTRIBUTE 
    'compatible.asm'          = '12.1.0.2',
    'compatible.rdbms'        = '12.1.0.2',
    'cell.smart_scan_capable' = 'true',
    'cell.sparse_dg'          = 'allsparse',
    'au_size'                 = '4M';

A sparse Oracle ASM disk group can store both sparse and non-sparse files, which makes it possible to store a test master database and Exadata Snapshots in the same disk group. However, because sparse grid disks are limited in size (to a maximum of 4 TB on a cell disk) and because there is no benefit in placing non-sparse files in a sparse disk group, you should reserve space in sparse disk groups for the sparse files associated with Exadata Snapshots and place the test master database in a regular (non-sparse) disk group.