Dell PowerVault ME4 Series Storage System Administrator’s Guide

Changing pool settings

Each virtual pool has three thresholds for page allocation as a percentage of pool capacity. You can set the low and middle thresholds. The high threshold is automatically calculated based on the available capacity of the pool minus 200 GB of reserved space.

You can view and change settings that govern the operation of each virtual pool:

• Low Threshold: When this percentage of virtual pool capacity has been used, informational event 462 is generated to notify the administrator. This value must be less than the Mid Threshold value. The default is 50 percent.
• Mid Threshold: When this percentage of virtual pool capacity has been used, event 462 is generated to notify the administrator to add capacity to the pool. This value must be between the Low Threshold and High Threshold values. The default is 75 percent. If the pool is not overcommitted, the event has an Informational severity. If the pool is overcommitted, the event has a Warning severity.
• High Threshold: When this percentage of virtual pool capacity has been used, event 462 is generated to alert the administrator to add capacity to the pool. This value is automatically calculated based on the available capacity of the pool minus 200 GB of reserved space. If the pool is not overcommitted, the event has an Informational severity. If the pool is overcommitted, the event has Warning severity and the system uses write-through cache mode until virtual pool usage drops back below this threshold.
• Enable overcommitment of pools?: This check box controls whether the allocated size of the volumes can exceed the physical capacity of the pool.
  NOTE:The above pool settings apply only to virtual pools.
  • When the overcommit feature is disabled, the host does not lose read or write access to the pool volumes when the pool reaches or exceeds the high threshold value.
  • When the overcommit feature is enabled, the storage system sends the data protect sense key Add, Sense: Space allocation failed write protect to the host when the pool reaches or exceeds the high threshold value. If the host is rebooted after the pool reaches or exceeds the high threshold value, the host loses read and write access to the pool volumes. The only way to regain read and write access to the pool volumes is to add more storage to the pool.

To check if the pool is overcommitted, hover the cursor over the pool in the pools table to display the Pool Information panel . If the Pool Overcommitted value is True, the pool is overcommitted. If the Pool Overcommitted value is False, the pool is not overcommitted. If you try to disable overcommitment and the total space that is allocated to thin-provisioned volumes exceeds the physical capacity of their pool, an error states that there is insufficient free disk space to complete the operation and overcommitment remains enabled.