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An oversubscription situation is automatically identified when:
  1. the storage pool is configured for thin provisioning (“thin storage pool”)
  2. the storage pool is oversubscribed, i.e. the total disk space visible to the hosts (subscribers) is greater than its actual capacity (this situation is normal for a thin pool since it is its very purpose)
  3. the storage pool actual consumed capacity has crossed the configured threshold.

Such a situation is highly critical because the inability to allocate additional space to a volume when requested by the subscriber host will lead to catastrophic data loss and corruption.

The following video (1:54) illustrates how you can use the Storage views to easily identify future capacity saturations within storage pools that can help you to avoid and manage oversubscriptions risks.

 https://youtu.be/l9Q2mxe6p60

To make sure no oversubscription situation is about to occur, administrators can check the Oversubscription Risk column available in the Storage Capacity View. By default, this metric displays:

  • "-" for non-thin pools
  • "No risk" for thin-pools that are not oversubscribed, i.e when the Storage Subscribed Capacity Percentage metric is lower than 100%.
  • "Warning" when the Storage Consumed Capacity Percentage metric is greater than or equal to 75% and the number of days before saturation is greater than or equal to 7.
  • "Critical" when the Storage Consumed Capacity Percentage metric is greater than or equal to 75% and the number of days before saturation is less than 7.

The threshold of the Storage Consumed Capacity Percentage metric can however be modified for each storage pool to warn administrators sooner about an oversubscription risk.

 To customize the oversubscription risk
  1. Access the Storage Systems page:

    1. Log on to the TrueSight console
    2. In the Navigation pane, click Capacity Views > Storage > Storage Systems
  2. Click the Storage Pools tab.
  3. Click the storage pool for which you wish to create thresholds.
  4. In the Related information section, click Thresholds.
  5. If the oversubscription risk indicator has already been customized, the line Storage Consumed Capacity Percentage will appear in the Thresholds table:
    1.  Click the  button to modify the threshold set for the Storage Consumed Capacity Percentage metric.
    2. Modify the Good Threshold and Warn Threshold fields.
    3. Click Save.
  6. If the oversubscription risk indicator has not already been customized:
    1. Click Add threshold.
    2. In the Metric search field, type Storage Consumed Capacity Percentage.
    3. Select Fixed value.
    4. In the Good Threshold and Warn Threshold fields, enter the value of your choice. You can for example enter 50 and 60 so that a warning is triggered when the Storage Consumed Capacity Percentage is greater than or equal to 860% and the number of days before saturation is greater than or equal to 7 and a critical situation is indicated when the Storage Consumed Capacity Percentage is higher than 60% and the number of days before saturation is less than 7.
    5. Click Save. As you can see in the example below, following this modification, the saturation risk for the DP Pool with a consumed capacity of 69% has changed to "17 days to saturation" and a warning is displayed in the Oversubscription Risk column.

To identify oversubscription situations

  1. Access the Storage Systems page:

    1. Log on to the TrueSight console
    2. In the Navigation pane, click Capacity Views > Storage > Storage Systems
  2. Click the Storage Pools tab.

  3. Filter the information displayed:
    1. by storage system to only list the storage system for which you wish to study the storage pools.
    2. by pool type to only display thin pools.
    3. by oversubscription risk to only display thin pools for which the risk is critical.

You now have all the information required to prevent oversubscription situations and unrecoverable data loss and corruption.