Datastore overprovisioning in Capacity-Aware Placement Advice overview

Use the Capacity Aware Placement Advice (CAPA) service to import data of datastore pools into the BMC Cloud Lifecycle Management infrastructure.

Overprovisioning of datastore elements is provided at the time of placement of a virtual disk, and must be defined as a percentage of the free space available on the target datastore.

Example

A datastore with 10 GB of free disk space and with 150% overprovisioning implies a total free space of: 10 GB x 150% = 15 GB.

Virtual datastore placement with overprovisioning

The overprovisioning setting in TrueSight Capacity Optimization is set as a:

  • Global setting for all datastores
  • Setting for a specific Datastore pool
  • Setting for a specific datastore

The value of the overprovisioning is retrieved as the first non-null value of:

  • Overprovisioning at the datastore level
  • Overprovisioning at the datastore pool level
  • Global overprovisioning

The Capacity-Aware Placement Advice service returns a different Return Status (error) code in each case to identify the exit status of the placement call. For more information, see Return Status (error) codes returned by the Capacity-Aware Placement Advice service.

After a successful placement, free datastore space is calculated by using the following formula:

freeAfterPlacement =
freeBeforePlacement * ( 1 - (candidateSize / freeWithOverprovisioning) )

Example 1

You have a 100 GB datastore, with a 75% threshold and an overprovisioning % setting of 150%.

For trying to provision a 20 GB vDisk, the following depicts how the algorithm behaves as the datastore fills up:

  • At 50 GB full, 25 GB free space is available - 20 GB vDisk will be allowed.
  • At 60 GB full, 15 GB free space is available - Since 150% of the free space is 22.5 GB, a 20 GB vDisk will be allowed.
  • At 70 GB full, 5 GB free space is available - Since 150% of the free space is only 7.5 GB, a 20 GB vDisk will not be allowed.

Example 2

A datastore has 10 GB of free space and an overprovisioning ratio of 150%.
You try to provision a candidate with a 12 GB vDisk:

10 GB * 150% = 15 GB.
This results in a successful placement of the candidate.

After the placement, the new free space available (till consumption data comes from the ETL) will be:

freeBeforePlacement * ( 1 – (candidateSize / freeWithOverprovisioning) )
= 10 GB * (1 – 80%) = 2 GB.

Where to go from here

To learn how to define datastore overprovisioning ratios at different levels in your cloud infrastructure, see: Viewing and configuring datastore overprovisioning

Related topics

Return Status (error) codes returned by the Capacity-Aware Placement Advice service

Affinity for Capacity-Aware Placement Advice overview

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