Sudden egress performance problem with QoS on C3560
We went live with a set of 3560G-48s a few weeks back. We have basic a basic policy map applied to some of the ports to DSCP mark select traffic, but a pretty stock setup other than that.
This week we noticed that large file transfers from our Gig connected EMC Celerra NAS to any of our NT systems set to 100 meg were horribly slow. Packet trace shows lots of TCP retransmits. Similar NT systems set to Gig have no problems talking to the EMC or anything else at any combination of port speeds. Non-NT systems on Gig or 100 have no problems with the EMC either.
Yes: "The EMC is at fault" is my first guess, too, but here is the thing: Removing the service policy on the client port resolves the problem. No more retransmit storms.
"sh platform port-asic stats drop CLIENTINTERFACE" shows increasing dropped frames for queue 1, weight 0 as the problem is occuring.
Anybody had this happend before, where mls qos works fine for weeks, then has a sudden problem with egress queues?
Re: Sudden egress performance problem with QoS on C3560
Thanks for the info, Michael! We are running 12.2(25)SEE1, and sh mls qos queue-set output shows that the defaults match the recommendations in the bug you referenced.
You did get me on the right track, though.
We found another server with the same issue. (2003 server.) Eventually, as I went to try retuning the output queues again, I noticed something interesting: For drop threshold1, drop threshold2, and maximum threshold, the value range showed "<1-3200>" instead of "<1-400>". The docs and defaults on the switches all showed 400 as the max.
I scaled the output queues to match the new ranges, and voila! No more drops, and great performance everywhere!
1) Is this new range documented somewhere, and I just missed it?
2) There should be no nasty side effects to this change, correct?
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