Vista and file copies over high latency links


My colleague Julius (who is going for the world record for time left between blog posts!) has been discussing this interesting Vista result recently. We tend to copy lots of images from the US to the UK daily, and previously used a Windows Server 2003 box to do that - not any more, in his own words (apart from a minor edit to remove a server name):


I love the fact that here in the UK, with 200ms latency to the US, I can use explorer from within Vista and drag and drop a 2.7GB ISO image to my local drive from a US based Windows 2003 Serve and it only takes 25-30 minutes to copy it down.

Using explorer (or even richcopy) on Server 2003, takes 3 ½ hours to copy the same image.

I thought you needed Vista\LH Server at both ends to get the improved network performance over latent links, but it looks like you don’t.  


Food for thought, I cant wait to test a Windows "longhorn" server to "longhorn" copy over the same link/distance...mind you with a near 7x performance gain I'm pretty happy at present 🙂

Julius asked for clarification on this and this was the answer received:


This is likely related to our new TCP Receive Window auto-scaling feature that automatically grows and shrinks the Receive Window size based on the bandwidth-delay product.  This is just a receive side technology, so even though the server is not running the new NetIO stack, the receiver can request up to a 16MB receive window.  This adjusts throughout the lifetime of the connections and the tuning is done on a connection by connection basis.  Previously (2003 and earlier releases) there was only a single system-wide registry key that statically set the TCP Receive Window parameter. 


Checkout this Cable Guy article for more details.


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