vSphere 5.0 Update 1 introduces a tool to manually reclaim deleted blocks

With today’s release of VMware vSphere 5.0 Update 1, included is an update to vmkfstools that enables administrators to manually reclaim deleted blocks on thin provisioned LUNs on VAAI capable storage arrays.

The new flag added to vmkfstools is “-y” and takes the percentage of the deleted blocks to reclaim as an argument.

You need to cd into the VMFS volume with the deleted blocks before you run the command.

For example:

# cd /vmfs/volumes/MyThinVol

# vmkfstools -y 70

This will reclaim 70% or the deleted blocks. Note that this works even though the UNMAP Primitive was disabled when you installed Update 1. It is time consuming though. My advice is to run this off-peak time and place the host in maintenance mode.

See VMware KB article 2014849 for details.


  1. Interesting – this seems like a useful addition to vmkfstools. I like the cryptic ending too – “My advice is to run this off-peak time and place the…” My guess: datastore in maintenance mode? 🙂

  2. Mostafa Khalil says

    Actually, it is “place the host in maintenance mode” 😉
    Somehow the post got truncated. Thanks for bringing it to my attention.
    More info in the KB that I published as well. I didn’t want to copy the full content of the KB.

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