I have been battling high amounts of outDiscards on ports connected to vmware and iscsi hosts. I have verified there is no speed/duplex mismatch. I am not seeing any interface errors on on the vmware or iscsi host.
We have brand new Cisco 2960-s switches. Before we migrated to the Ciscos we were using 3com switches without error.
The only thing that has changed is on the vmware hosts trunking iSCSI traffic on the same physical port as the rest of the traffic. Could this cause this problem or am I missing something else?
I just cleared the counter errors a few minutes before:
Gi0/15 0 0 0 0 0 144 <------ iscsi host interface
sw1.e1#sh int gi0/15
GigabitEthernet0/15 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 1caa.0728.210f (bia 1caa.0728.210f)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:00, output hang never
Last clearing of "show interface" counters 1d00h
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 144
The output shows a lot of too large frames in both directions. This may be the cause of your problem.
Expl: Because you are now tagging the iSCSI frames, their size will grow with four bytes. Depending on the actual MTU sizes, this may be slightly too large. The following link contains some information on the subject:
Thanks for the input. I disabled all trunking for the storage interfaces last night. I am still seeing high discards on one of our vmware servers today though. There are no discards on the other vmware server or the iscsi SAN.
I cleared the counters 6 hours ago:
Gi0/14 0 0 0 0 0 100394
Any other Ideas? I was looking to see if I could set the mtu to 1500 on the specific port on the switch but it doesnt look like Cisco has an option for that.
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