Catalyst 3750G and iSCSI Storage Array

[Delmiro Campelo]

Good morning support community,

I  have a quick question that I'm hoping you can shed some light on. I'm  planning to build a SAN using a pair of 3750G (early generation). One of  the best practices that I'm seeing from the vendor is to set the mtu on  the switch to 9000 globally. so here is my concern.

1.  Can I run iSCSI traffic on vlan A and network traffic on vlan B on the  same switch with MTU of 9000 ? would that create any issues for network  traffic?

2. What would happen to network traffic with an mtu 1500 ? would it get dropped or slowed?. 

We are on a tight budget so I don't have that much wiggle room for another pair of 3750s.

Thanks,

Delmiro

[Leo Laohoo]

1.  Can I run iSCSI traffic on vlan A and network traffic on vlan B on the  same switch with MTU of 9000 ? would that create any issues for network  traffic?

On a Catalyst 3K, you will not be able to increase the MTU on a per-interface level.  If you want to increase the MTU, ALL INTERFACES will have their respective MTU increased.

2. What would happen to network traffic with an mtu 1500 ? would it get dropped or slowed?.

Wouldn't make any difference what MTU you are going to be using.  At the end of the day, when your high-speed-and-hitless iSCSI starts pushing traffic across your Catalyst 3K, the switch will be unable to withstand the amount of data traffic and will start dropping traffic like there's no tomorrow.  Catalyst 2K and 3K switches have very shallow buffer and were not designed for high-speed-and-hitless traffic.

You'll need 4500R+E, 6500E or Nexus 2K paired with 5K/K.