[c-nsp] Jumbo frames on certain VLANs with UCS fabric?

[David Hubbard]

Hi all, I'm working on deploying a UCS system using
iscsi to an EMC with only a pair of 4900M's in
between.  I'm having a bit of trouble wrapping my
head around what I need to do to enable jumbo frames
to make it from end to end on the storage vlan.

What I've got so far:

1) Two redundant UCS fabric interconnects are each
in end host mode and each dual-home to the two 4900M's
at ten gig.

2) Within the UCS configuration, there is a virtual
nic defined as mtu 9000, the rest of the virtual nics
are defined as mtu 1500.

3) The 4900M's have a storage vlan configured with an
mtu of 9000.  All other vlan's are default 1500.

4) The ten gig interfaces to the UCS are set as mode
trunk but not mtu 9000 (I think this is an issue?).

5) The ten gig interfaces to the EMC's two service
processors on each 4900M are configured as
'switchport access vlan...' and 'mtu 9000'.

6) The two 4900M's have a trunk between them carrying
all vlan's.  (This may be an issue too?)


show int on the interfaces to the UCS fabrics and the
switch to switch trunk are both showing mtu 1500.  Do 
I need to set all of those interfaces to 9000?  I tried 
that, but did not test the EMC connectivity in between
because I noticed as soon as I set that I got a bunch
of MTU_Mismatch showing in "show vlan mtu" and I was
worried I was about to create a big problem.  Or, is 
it ok to have the mismatch there because any device 
talking on the 1500 byte vlans would not generate a
larger packet anyway but devices on the 9000 byte vlan
are free to talk jumbo and the interfaces will transport
it because it's mtu 9000 all the way through, including
the switch to switch trunk?

Thanks,

David