If you used a thin-provisioned storage device with a legacy ESX/ESXi host (version prior to 5.0), you can retroactively reclaim accumulated free space for the device.

Upgrade your host to ESXi 5.0.

Upgrade a datastore deployed on the thin-provisioned device to VMFS5.

1

On the ESXi Shell, change to the datastore directory by using the cd /vmfs/volumes/datastore_name command.

2

Reclaim a specified percentage of free capacity on the VMFS5 datastore for the thin-provisioned device by running vmkfstools -y %.

% is an integer between 1 and 99. It represents a percentage of VMFS free capacity to be reclaimed. The recommended value is 60.