About Disks

The Disks option on the Storage Details page shows the allocated and unallocated storage for all the disks and disk partitions on a host. All disks are listed including virtual disks from external storage systems such as EMC Storage Array.

Note: Overhead information for virtual disks is not instrumented nor presented.

For a disk to be deployed for usage, the disk must first be formatted. After formatting, the disk can be configured (using vendor-specific configuration utilities) to have one or more partitions.

A disk or disk partition can be associated (using vendor-specific configuration utilities) with exactly one entity from one of the upper layers (volumes, Oracle ASM, databases, and file systems) on the host. When an association exists for a disk or disk partition to an upper layer entity, it is reported as allocated space in Enterprise Manager.

Formulas for Allocating Disk Space

The disk space is allocated using the following formulas:

Allocated space in the disk equals (=)

Sum of the size of the allocated disk partitions if the disk has been partitioned
or 
Size of the disk if the disk is allocated to an upper layer entity
otherwise
0 (zero)

Unallocated space in the disk equals (=)

Size of the disk 
- Allocated space in the disk

Unallocated space in the disk partition equals (=)

Size of the disk partition if it is not allocated
otherwise
0 (zero)

Allocated space in the disk partition equals (=)

Size of the disk partition if it is allocated
otherwise
0 (zero)

See About Storage Computation Formulas to learn how disk layer level summary attributes are calculated for associated hosts.

About Disks

Formulas for Allocating Disk Space

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