Windows 2003 Large File Copy Performance Drops Off

All,

I've got a strange problem trying to copy large files. All weekend I've been trying to solve this problem and can't seem to find a newsgroup posting or KB article on point. After some trial and error I've narrowed the problem down to copying a single 5-8 gig file (it doens't matter which one). For the first ~3 Gigs (or maybe its first 3-4 minutes) I get 20-30% NIC utilization, then when the magic threshold is hit the speed drops off to about 0.5%. The drop is sudden and consistent.

Some other background:
- Source is Windows 2003 Standard
- Desitnation is Windows 2003 x64 Enterprise
- Each server has a gigabit NIC
- Links seem to be 1Gps full duplex
- Both servers have latest NIC drivers
- Both servers have SP2 & up to date on fixes
- Tried multiple Network Cables with the same results
- Tried multiple gigabit switches (nothing fancy, just unmanaged switches) with the same results
- isolated servers on their own switch with same result
- servers are doing nothing other than the file copy
- disk activity seems to be minimal
- No anti virus running
- Servers are just in workgroup

- Problem crosses problem doesn't is experienced using Windows Explorer, Copy, Robocopy, and even FTP
- Using mapped drive or UNC is no different
- Some have mentioned large file copies chewing up available ram, then slowing --- not the case here. Machines are using between 200-400 Megs of ram but have 2 gigs (source) and 8 gigs (destination) installed
- duplex mismatch -- doesn't seem to be the case here otherwise i wouldn't be consistently getting ~250Mbs for the first 5 minutes.



Thanks in advance if you can provide any help. I've been tearing my hair out for the past few days trying to track this down. I've got a close to a terabyte to transfer and speeds like that of a 56k modem is kind of a problem.

Thanks
-eric

.

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