Large I/Os are split into 64 KB units when using LSILogic Driver (9645697)
Refer to the section 126.96.36.199 Large Block Size Support in the LSI Fusion-MPT Device Management User's Guide
Note: The preceding link was correct as of November 5, 2014. If you find the link is broken, provide feedback and a VMware employee will update the link.
For more information see Guest Operating System Storage Considerations in the Performance Best Practices for VMware vSphere 5.0.