iSCSI performance issue at ESXi

Recently, I experienced abnormal situation.



My test lab is configured one iSCSI storage server and two ESXi servers.

after something test, I had reconnected UTP cables of servers.

then unbelievable situation was occured!



iSCSI storage performance go slow down approximate 5~6MB/s.

I didn't accept this. first time, I had doubted my switch. but It was not cause.

second, I checked ESXi server. because I use software iSCSI adapter and Realtek NICs.

I suspected it is cause of problem. but also it was not cause of issue.

third, I deleted iSCSI LUN and rebuild it. but anything changed.

then, I connected iSCSI storage to Windows 7 iSCSI initiator.

and I watched that It works good. transfer peformance was normal status.



Fortunately and incidently, I discovered what was the cause of the issue.

I use two type of Realtek NICs. one is old PCI type 1 Gigabit NICs

and another one is new PCIe type 1 Gigabit NICs. It was the point.



of course PCI bus interface has plenty of bandwidth for Gigabit network.

but ESXi didn't think like that. just PCIe type NICs and onboard NICs works fine.

I think it was VMware's compatibility issue with PCI type NICs.

after changing from PCI type NIC to PCIe type NIC, performance was recovered. (60~80MB/s)



I have searched this issue at many online communities.

but anyone didn't mention about it.

of course this problem is not happen always.

because, anyone use Realtek NICs on Servers.

but someone who has Test lab like me, maybe will experience this issue.



Check your NIC's bus type if it use PCI or PCIe bus interfaces.



Regards.