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VMM shows the wrong total disk size for a storage pool

Symptoms

After you add a storage array to Microsoft System Center 2016 Virtual Machine Manager (VMM) through SMI-S, the displayed value for the total pool size (Total Managed Space) is incorrect even though the LUNs and pools are displayed correctly. The total size is shown as much larger than the current capacity of the storage device.

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Cause

This issue occurs because VMM displays the total pool size based on the type of underlying pool that is defined by the storage device. When this issue occurs, the pool type that is defined is causing the maximum possible expansion of the pool to be returned as the displayed size.

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More Information

Per SNIA standards, we use the following properties to compute storage pool capacity:

  • Total Managed Space
  • Space limit
  • Space limit determination　

The space limit determination can have any of the following values:
  • Fixed (or Allocated)
  • Quota
  • Limitless
Fixed: For a Fixed (primordial) pool, the capacity can be considered to be the total managed space.

Quota: For a concrete pool, space limit serves as an administratively defined limit on the capacity that may be used to create or expand child elements.　

Limitless: The block server does not limit the capacity for creating and expanding child elements.

A client that supports thin provisioning should not use the space limit property. However, for compatibility with other clients that do not support thin provisioning, heuristics are used to set the space limit. One of the heuristics that is used is the value of the largest volume that is supported by implementation. Therefore, for limitless case, the provider may use the heuristic to set the space limit value to return the max pool capacity.

To report the pool size, VMM reads from the storage device the Total Managed Space (for Fixed) or Space limit fields (for Quota and Limitless).

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Applies to

This article applies to the following:
  • System Center 2016 Virtual Machine Manager

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Keywords: kb

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Article Info
Article ID : 3198630
Revision : 1
Created on : 1/7/2017
Published on : 11/22/2016
Exists online : False
Views : 92