According to VMware's Thin Provisioning data sheet, there is ZERO performance penalty when disks are thin provisioned.

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<p class="MsoNormal"><span style="font-size: 10pt; font-family: &quot;MyriadPro-Light&quot;,&quot;sans-serif&quot;;">“Thin provisioning of virtual disks allows virtual machines on VMware ESX™ hosts to provision the entire space required for the disk’s current and future activities, but at first commits only as much storage space as the disk needs for its initial operation. It achieves this <strong><span style="color: red;">with zero performance impact</span> </strong> ,continuous service availability and complete data integrity.”</span></p>

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<p class="MsoNormal"><span style="font-size: 10pt; font-family: &quot;MyriadPro-Light&quot;,&quot;sans-serif&quot;;">So for those of you who are rapidly running out of space, but shied away from Thin Provisioning for fear of a performance hit, you might want to rethink things. And if you have the capability and licensing to use Storage vMotion, you can Thin Provision your disks as you move them. Recover that space!<a href="http://www.vmware.com/files/pdf/thin_provisioning_datasheet.pdf" target="_blank"></a>
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