Monitor automatic unmap I/O issued by ESXi

Products

• VMware vSphere ESXi

Issue/Introduction

Check the automatic unmap I/O per VMFS6 datastore/volume issued by an ESXi host.

Check if automatic unmap I/O has been issued by an ESXi host. 

Environment

VMware vSphere ESXi 6.5
VMware vSphere ESXi 6.7
VMware vSphere ESXi 7.0.x
VMware vSphere ESXi 8.0.x 

Resolution

• On an SSH session to an ESXi host, access the VSI shell prompt by running:

vsish

 

• Then navigate as follows:
  
  /> cd /vmkModules/vmfs3/auto_unmap/volumes/

 

• To list the VMFS6 datastores/volumes for which unmap is being issued, run:

/> ls

 

• To view the automatic unmap stats for a specific datastore:

/> get /vmkModules/vmfs3/auto_unmap/volumes/<datastoreName>/properties

 

• Alternatively, directly run:

vsish -e get /vmkModules/vmfs3/auto_unmap/volumes/<datastoreName>/properties

 

Sample output:

Volume specific unmap information {
   Volume Name                  :<datastoreName>
   Volume: Num SchedQs          :1
   FS Major Version             :24
   Metadata Alignment           :4096
   Allocation Unit/Blocksize    :1048576
   Unmap granularity in File    :1048576
   Volume: Unmap IOs            :1446
   Volume: Unmapped blocks      :85135
   Volume: Num wait cycles      :1
   Volume: Num from scanning    :3948
   Volume: Num from heap pool   :391
   Volume: Total num cycles     :961963
   Unmaps processed in last minute:0
   Volume: Unmap SchedQ IOs     :1446
}

Note: Statistics are reset on ESXi host reboot.

 

Additional Information

Non-zero values for Volume: Unmap IOs and Volume: Unmapped Blocks indicate that automatic unmap I/Os have been issue by a host for a given VMFS6 volume since last reboot. 

 

Check the output at intervals (e.g. daily) for incrementing values of  Volume: Unmap IOs and Volume: Unmapped Blocks to confirm ongoing issue of automatic unmap I/Os to the volume on the host. 

 

Unmap metrics can also be monitored via the VAAI stats on esxtop - see  Monitoring VMware vSphere Storage APIs – Array Integration using esxtop and maintaining the status as enabled. Note, however, that esxtop unmap metrics will include any manual unmap IOs issued, as well as automatic unmap IOs.