Deleting virtual machines on a vSAN datastore does not fully recover the used space
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Deleting virtual machines on a vSAN datastore does not fully recover the used space

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Article ID: 412979

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Updated On:

Products

VMware vSAN

Issue/Introduction

Symptoms:

  • Post deleting virtual machine which resides on vSAN datastore, it appears that the deleted space is not re-claimed.

  • The space utilization of vSAN datastore does reduce, but not completely to match the space usage of the deleted virtual machine.

Environment

VMware vSAN 7.x

VMware vSAN 8.x

This KB is applicable only for vSAN datastore with 'Compression only' or 'Deduplication & Compression' enabled.

Cause

  • vSAN can perform block-level deduplication and compression to save storage space.

  • When deduplication and compression is enabled on a vSAN all-flash cluster, redundant data within each disk group is reduced.

  • Deduplication removes redundant data blocks, whereas compression removes additional redundant data within each data block. These techniques work together to reduce the amount of space required to store the data.

  • By doing this, the vSAN datastore's total physical storage consumption is reduced, and its logical storage utilization is maximized.

  • Considering the above information, when a virtual machine is deleted from a vSAN datastore where 'deduplication and compression' or 'compression only' is enabled, the virtual machine's complete space usage is not expected to be freed from the vSAN datastore.

  • This is because the VM's data would have been stored in a deduplicated and compressed state.

  • The space utilization shown in the vCenter UI is the physical storage utilization and not the logical one. (vSphere Client > vSAN Cluster > Monitor > vSAN - Capacity and also at vSphere Client > Datastore tab > Select the vSAN datastore)

  • The deduplication of the virtual machine's data depends on many factors, including the type of data stored and the number of duplicate blocks.

  • Due to this there is no formula to manually calculate the space which would be recovered on the physical storage on deletion of a virtual machine.

Resolution

  • No action is needed here.

  • The storage space used by the virtual machine has been freed from vSAN datastore.

Additional Information

Documentations explaining the space efficiency technologies in vSAN:

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