I'm trying to make sense of the (thin provisioned) disk space on VMware ESXi 4.1 (using vSphere Client). The numbers I see don't add up and don't make sense.

Looking at the machine properties for an example VM, I see Hard disk 1 takes up 20Gb on datastore1 - and there are no other hard disks for this VM. However, the Summary tab for the VM has the VM using 24Gb on datastore1 and datastore2 - what's the extra 4Gb for? Also, the only thing on datastore2 is CD ISOs.

On top of this, this running VM instance is only taking up 2.23kb on disk according to the virtual host's Virtual Machines tab.

How can a full installation of Ubuntu Lucid Lynx take up 2.23kb? Would be a marvel... Even with data deduplication (which I wonder if VMware even supports) there would be a lot more than 2kb of unique data.

Ultimately, I want to be able to get an accurate report on amount of disk provisioned for each datastore (and per VM) and the amount of disk used (and per VM). Right now, it seems the only thing I can get from the command line is the total amount of disk used; any way to get the rest? I couldn't find any. The GUI has varying numbers as I reported.

1 Answer 1


The extra space corresponds to the memory (RAM) footprint of the VM (It's the .vswp file). You most-likely have 4GB of RAM in that VM. Also on the datastore tab, click the "Refresh" link to update the values to reflect current utilization.

  • 1
    +1, it's the pre-allocated swap space for the VM and is directly related to the memory allocated to the VM - give the VM 16GB and it'll add 16GB to the disk space required, and it won't 'thin' it, it needs to KNOW it's available for if/when the host gets contended.
    – Chopper3
    Sep 23, 2011 at 17:14
  • Looks like those 2k numbers were because the storage numbers had not been refreshed. It appears that you have to refresh each VM individually, and that there's no way to refresh all VMs at once - nor is there a way to do it from the VM host Virtual Machines tab in vSphere Client.
    – Mei
    Sep 23, 2011 at 22:34

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