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November 3rd, 2023 06:08

Unmap Space Reclamation Operations on Dell SCv3020 VMFS5

Trying to see if i can run both unmap commands consecutively. Will this adverse affect the disk operations on the Virtual machines? I have 4 hosts and baout 40 running VMs

1st Command:

esxcli storage vmfs unmap -u XXXXX - n 1024

2nd Command

esxcli storage vmsf unmap - u xxxxx 

I know the second command will check for the default 200MB blocks while the 1st command will check for 1MB blocks.



2.1K Posts

November 3rd, 2023 10:29

Hi, I found two articles that maybe related. What I took away from these is the following. the esxcli storage vmfs unmap command can free up storage blocks that are not used on a VMFS datastore for a device with thin provisioning. However, this command has some restrictions and challenges, especially on VMFS5 datastores . For instance:

  • The unmap command from the guest operating system to the VMFS5 datastore can only reach the array if the virtual machine satisfies some conditions.
  • The unmap command generates temporary hidden files on the top level of the datastore, with names following the .asyncUnmapFile pattern. The space allocation for the temporary files depends on the block size of the VMFS file system and the reclaim unit value.
  • The unmap command can send many unmap requests at once, which can lock some of the resources during the process and affect the performance of the virtual machines.

Therefore, it is advisable to run the unmap command when the traffic is low or when the virtual machines are not running. Running both unmap commands one after another might not be needed, as the second command will scan the same blocks as the first command,

Reclaiming VMFS deleted blocks on Thin Provisioned LUNs (2057513) (

Space Reclamation Requests from Guest Operating Systems (


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