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19502
Q about jumbo frames and setting up separate vlan
Why do you recommend to set aside a VLAN for jumbo frames for data between ISCSI hosts and the EQ?
This post is more than 5 years old
9 Posts
0
19502
Why do you recommend to set aside a VLAN for jumbo frames for data between ISCSI hosts and the EQ?
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Net-Paws
3 Posts
1
September 27th, 2010 12:00
There's another reason to avoid the defaul VLAN: with Cisco switches VLAN 1 only supports standard frames (1500 bytes). Since it's the default VLAN, Cisco will attempt to deliver every packet, including jumbo frames. When the switch is busy, larger packets may be dropped (leading to inconsistent behaviour with jumbo frames). The MTU defined for other VLANs will be enforced (correct behavior will pass jumbo frames every time, OR none of the time).
This frame inconsistency can be difficult to troubleshoot - I had two W2K3 servers connected to my SAN. Both servers could discover, connect, and partition their volumes, but one would always disconnect when I went to format it (the other worked). The working server connected via standard frames while the problematic one connected at 9000 bytes. Setting the server's NIC to standard frames immediately resolved the issue (further testing with a different VLAN showed that both servers could work properly with jumbo frames).
I was able to reproduce those results with a PowerConnect switch, and understand many vendors follow Cisco's lead regarding this behavior.
JOHNADCO
847 Posts
0
September 24th, 2010 16:00
Vlan becasue you want iSCSI traffic as isolated as possible. Jumbo frames becase it can offer better throughput. To try to do all jumbo frames on your LAN network would be very difficult to get it working end to end on all devices attached.
sandramunoz999
9 Posts
0
September 24th, 2010 16:00
Thanks a lot for your quick reply.
Is it just a matter of configuring a VLAN on the blade switch that connects the EQ with the hosts , and assigning the vlan to those ports?
Does anything need to be done in the EQ?
We have had performance issues that have improved after a hotfix was installed on the hosts, but we are not following the VLAN 1 recommendation.
JOHNADCO
847 Posts
0
September 24th, 2010 16:00
Truth be told? I don't like the Vlan method. I actually use different switches for each different subnet on each different iSCSI port on the san. So multiple isolated networks. I think most Equlogic sans use all the connections in the same subnet though.
sandramunoz999
9 Posts
0
December 7th, 2010 12:00
Thank you all! we have not had performance issues since we changed the recommended parameters.