How Oracle Works on Exadata - Oracle Exadata Recipes: A Problem-Solution Approach - page 59

On Exadata, grid disks are the logical storage entities on the storage cell upon which ASM disks can be discovered
and ASM disk groups can be built. Let's look at some attributes of the grid disks that make up the DATA_CM01 ASM disk
group from one of the Exadata storage cells, cm01cel01 :

CellCLI> list griddisk where name like 'DATA_CD_.*' attributes name,asmDiskGroupName,asmDiskName,
cellDisk,size
DATA_CD_00_cm01cel01 DATA_CM01 DATA_CD_00_CM01CEL01 CD_00_cm01cel01 284G

DATA_CD_01_cm01cel01 DATA_CM01 DATA_CD_01_CM01CEL01 CD_01_cm01cel01 284G

DATA_CD_02_cm01cel01 DATA_CM01 DATA_CD_02_CM01CEL01 CD_02_cm01cel01 284G

DATA_CD_03_cm01cel01 DATA_CM01 DATA_CD_03_CM01CEL01 CD_03_cm01cel01 284G

... Additional grid disks omitted

CellCLI>

We can see that each grid disk belongs to the DATA_CM01 ASM disk group and that the ASM disk name is displayed
in the third column. This disk path/string corresponds to V$ASM_DISK.PATH . Furthermore, we can see which cell disk
each grid disk is part of and the grid disk size.
Each of the grid disks resides on an Exadata cell disk with a similarly named cell disk name, prefixed by
DATA_ . Again, this is a common but not required convention; when an administrator builds Exadata grid disks,
he or she typically uses a prefix clause to seed a grid disk prefix and append the cell disk name.
The size of each grid disk is displayed in the sixth column. Note the uniform grid disk size. Uniform grid disk
sizing is not required, but it is recommended to ensure database extents are evenly distributed across grid disks and,
ultimately, ASM disk groups.

How It Works
Oracle uses ASM exclusively on Exadata for database storage. ASM disk groups consist of Exadata grid disks, and grid
disks are built on Exadata cell disks. The general flow of creating Exadata database storage looks like the following:

• Install and validate the Exadata Database Machine.

• Create cell disks. This is typically done at the time of installation by Oracle ACS, but an

administrator can reconfigure cell disks at a later time. Grid disk interleaving is done at the cell
disk level.

• Build grid disks on Exadata cell disks. When building grid disks, pay special attention to the

end goal, which is Oracle ASM storage. As an administrator, you want to ensure that grid disk
sizes and placement is in alignment with business objectives.

• Create ASM disk groups with Exadata grid disks.

In short, grid disks are created on cell disks and represent the storage available for ASM disks. When you create
ASM disk groups, the devices you use are grid disks, and grid disks are the disks exposed and available to Oracle ASM.
Exadata administrators are encouraged to strive for equally sized, well-balanced grid disk configurations. Doing
so enables Exadata to maximize disk I/O bandwidth, I/Os per second, and ultimately ensure a well-balanced, high-
performing storage platform on Exadata. Oracle truly makes this effort easy on Exadata—contrary to some other
storage array vendors and the associated administrative processes, with Exadata the process of creating the most
robust, balanced, and high-performing storage configuration is also the simplest and involves the least amount of
keystrokes. After creating cell disks, the administrator would create grid disks with a unique grid disk prefix, starting
with the “most important” storage so that the extents reside on the outermost disk tracks. In a single cellcli or dcli
command, you can create grid disks that span every cell disk and every storage cell. Then, the administrator simply
creates ASM disk groups using a wild-carded storage server InfiniBand IP address and wild-carded Exadata grid disks.