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Why do I see a high output queue length in perfmon when the network adapter is saturating a WAN link? If a file is transferred across the 10Mbps link, the server will max out the connection and all other network operations come to a crawl. Ping starts to rise to 600ms. What can I do to prevent/fix this?

This is a Windows 2000 VM.

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1 Answer 1

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Output queue length == number of packets waiting in line to be sent.

So, when you've maxed out your link, and still have "stuff" to send, it goes into the output queue, since it can't be immediately sent (on account of the link being at bandwidth capacity). Also why your ping response time gets high - those network packets have to wait in line too.

To fix this, you can get a fatter pipe, send less stuff, or (probably the best option) throttle your send rate as to avoid sending faster than your link can handle.

You can also try updating firmware and network drivers (as in the linked article), but as you've already stated that your WAN is saturated, that's not going to help. You're trying to send too much, too fast, so you end up with a queue. Better than having the traffic dropped.

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Thanks. I wasn't sure if updating the firmware + drivers would help with the saturated WAN. –  Tanner Aug 16 '12 at 16:58

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