You should take a look at Scott Lowe's post about dvs + Jumbo Frames: http://blog.scottlowe.org/2009/05/21/vmware-vsphere-vds-vmkernel-ports-and-jumbo-frames/
There's a few things you need to do to get that working, it's not so straight forward
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William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at: http://engineering.ucsb.edu/~duonglt/vmware/
Getting Started with the vMA (tips/tricks)
Getting Started with the vSphere SDK for Perl
VMware Code Central - Scripts/Sample code for Developers and Administrators
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