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I am running an 03 box with shares active. When uploading to the share, the speed is average. About 15-20 mbps.. This server is connected directly to 2 other machines accessing the server. When uploading to another server the connection speed is twice that of the direct storage. When uploading s massive folder, 250 GB, the upload will start as normal, but as it progresses it drops in speed. Now it is sitting at around 2-7 Mbps. Any ideas on howIi can boost the transfer rate? On a side note, the download speed is great. It is a speed that you would expect from this setup, the main problem is uploading and what is causing the extreme slowness in speeds. Any help would be great.

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Can you tell us more about the hardware on the server? –  Luis Ventura Dec 23 '10 at 8:20
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1 Answer 1

It depends on your hardware and the file structures you are copying. Copying one big file will generally be faster than copying many small files. When you are copying directory structures with thousands of files over a network connection on a file by file basis the transfer rate will always be a lot slower than a single large file copy.

However with very large files Windows 2003 can find itself in a situation that catastrophically affects both transfer rate and overall performance on the server. Windows 2003 buffers incoming network file copies to RAM and flushes them disk in the background as fast as it can. If your network connection is faster than your disk subsystem can keep up with this can lead to extreme amounts of RAM being consumed to store the buffered data. It's not hard for this to happen with Gigabit ethernet if you have only one disk or a small number of disks with RAID 5 behind the volume you are copying to. If your files are small this isn't too damaging as the copy simply slows down as each file gets written out before the next one can be started (for the most part) but if you are copying really large files under these conditions then the server will start to page out everything it can which will lead to severe performance problems if the files you are copying are significantly larger than the amount of free memory you started with.

Other activity on the server will impact this too - if the server receiving the copy is carrying out any other IO at the same time then this will cause the problem to occur much more rapidly. Your comment that the network copy is initially faster than local copies to direct attached storage strongly indicates to me that this is part of not all of your problem.

This behaviour has been fixed with Windows 2008 but the changes weren't universally welcomed as they appeared to slow down many copies that never triggered the worst case behaviour.

If this is the case then faster disks will help - if the disks can keep ahead of the network transfer rate then the problem wont happen. Moving to Windows 2008 should help but you may see slower initial copy speeds but better overall average transfer rates when dealing with large files in particular.

This article by Mark Russinovich about the changes in Windows Vista's copy behavior discusses the Windows 2003 issue if you want to really get to the root of it.

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