I recently had an issue where my ESX servers would continuously drop and re-connect their iscsi connections to an EQL PS6000.
The EQL was set with MTU 9000 (default), Dell 6248 switch was set for 9000 MTU, both the vSwitch, and the vmknic were set 9000 MTU.
I would see the ESXi servers login to the EQL box and it would show the connection was using Jumbo Frames, however, after a few seconds, my EQL would show the ESXi box disconnected (connection reset by peer) and then almost immediatly it reconnected (again showing Jumbo Frame connection).
This behavior would happen continuously, which ultimatly made the ESXi box unresponsive. The VMs were running and would respond to pings, but I could not get onto the console, nor could I get in and change any settings.
I could reboot the device (after much wait time), but the ESXi box would then hang while trying to make the iSCSI connections. ( I coudl see on the EQL box the constant connect/disconnect).
I was finally able to turn off the machine, unplug the physical nic the vmknic was associated with and start up with no iSCSI volumes. I could then change the settings on the vSwitch and vmknic to 1500 MTU. Once I did this, and did a re-scan of the adapter, the volumes were found, and no disconnects.
Everything seemed to work great.
So my question is, what am I missing?
- Each iSCSI software adapter is associated with a physical nic.
- The iSCSI vSwitch and port group are set to MTU 9000
- The port on the Dell 6248 Switch is set to MTU 9000 (for each pNic connection, and for each EQL connection)
- The EQL iSCSI port is set for 9000 MTU
Did you verify that your vmknic for iSCSI traffic are really used (iSCSI bindings or/and VLAN segmentation)?
Also you can do some checks with vmkping to see if jumbo frames really work. Rickard wrote a nice article about this: http://rickardnobel.se/archives/992
The switch is isolated from the rest of the network, and I do have the iSCSI bindings set for that particular nic.
Thank you, I'll check out the document.
I switched the ESX portion back to MTU 1500 and everything works fine (with the switch and EQL box still on MTU 9000). The EQL box shows a standard connection, not jumbo connection.