With the release of vSphere 5.0, VMFS (VMFS-5) block size has been fixed at 1 MB. It's not settable at the user level, as far as I know, like vSphere 4.x.
Forgot the link: VMware KB: Frequently Asked Questions on VMware vSphere 5.x for VMFS-5
All the best,
Mike
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Mike Brown
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Message was edited by: Mike Brown