Here is a picture that perfectly describes my situation:

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Is there some way I can smooth this transfer out to be near 90% usage by increasing a buffer somewhere? It seems like windows grabs a chunk of the drive, empties the cache, then waits for the drive to grab another. Instead of pulling data off the disk as constantly.


Windows Small Business Server 2011 hosted on an ESXi (.vmx and .vmdk are on mirrored SSD's) box pushing a 10gb file to a FreeNAS machine (capable of 100MB/s transfers from other clients) over iSCSI (need direct block access for SBS2011 backups.)

Looking in the FreeNAS monitoring it's averaging around 600Mb/s.

  • you've got a lot different technologies working there, can you identfy where the bottle neck is? How does a non-ESXI windows box behave? – The Unix Janitor Mar 6 '12 at 20:12
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    I don't see any evidence that it's not pulling the data off the drive constantly. Do you have any reason to suspect that during the times when the network traffic is lower, the disk I/O throughput is also lower? (Imagine if you're receiving pumpkins one at a time and sending them out in trucks of 1,000. You'll see a pause, then a truck of 1,000, then a pause, then a truck of 1,000. But pumpkins are arriving at an even rate. More trucks wouldn't make pumpkins arrive faster nor does pauses between trucks indicate pauses in arrival.) – David Schwartz Mar 6 '12 at 20:54

Have you checked for a duplex mismatch on your network? That misconfiguration allows devices to work and seem okay under low load, but as soon as they start communicating at any real speed, the rate plummets. http://en.wikipedia.org/wiki/Duplex_mismatch


You may be running into a network buffering issue somewhere. It may be counter intuitive, but shrinking your maximum network window size may help.

Check these links http://netalyzr.icsi.berkeley.edu/links.html

I have seen duplex mismatch slow down transfers. This tends to be a one way effect. Transfers run fine in one direction, but slow in the other. This can be tested by timing the transfer of a large (1-2 MB) file in both directions.

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