Storage Administration - Oracle Exadata Recipes: A Problem-Solution Approach - page 240

'cell.smart_scan_capable' = 'TRUE',
'au_size' = '4M';

Diskgroup created.

SQL>

In this example, we're creating a four-disk ASM disk group using two grid disks from two of our storage cells.
Note that in this case, we need to specify a failure group and the overall syntax and planning becomes a bit more
complicated as compared to cases in which wild-carded cell server IP addresses and grid disks prefixes are provided
in the CREATE DISKGROUP statement.

How It Works
The task of creating Oracle ASM disk groups entails not only using the CREATE DISKGROUP statement, but also
understanding the relationship between ASM disk groups and Exadata grid disks. To learn more about the overall
storage entity relationships on Exadata, please see Recipes 3-1 and 3-2.
In order to create ASM disk groups, you need available, unassigned Exadata grid disks.

■ Note please see recipe 9-3 to learn how to find exadata grid disks that are not assigned to an aSm disk group.

Once you identify candidate grid disks, use the CREATE DISKGROUP command to create your ASM disk groups.
Here are some of the more important considerations to think about when creating ASM disk groups on Exadata:

CREATE DISKGROUP syntax not only offers the
most terse command syntax, but also ensures your ASM disk groups are spread evenly across
your Exadata Storage Server disks.

• Simplicity is best on Exadata. Using wild-carded

• Oracle automatically assigns the proper failure groups, depending on your redundancy level,

when you create ASM disk groups spanning all storage cells and grid disks.

• When capacity planning, take your redundancy specification into consideration. Normal

redundancy will have the effect of reducing your usable storage to half the raw capacity, and
high redundancy will shrink it to a third of your raw disk capacity.

• Take the time to plan grid disk prefix names and overall grid disk configuration in the context

of your desired ASM disk group design.

compatible.asm and compatible.rdbms attributes when • Make sure to set the appropriate

creating ASM disk groups.

• Whenever possible, use a 4 MB extent size when creating disk groups on ASM storage.

One of the nice things about ASM storage on Exadata is that the planning aspect is relatively straightforward
and automatically handles some of the more complex aspects of ASM storage planning. As an Exadata administrator,
you simply need to size your grid disks appropriately (ensuring to spread evenly across storage server), give them a
meaningful prefix, and then build ASM disk groups on a wild-carded set of Exadata grid disks.