You should be able to speed up backups from UNC shares in Windows NT 3.5. The problem is the case of a value in the Registry.
In Registry Editor, open the following HKEY_LOCAL_MACHINE key:
System\CurrentControlSet\Services\LanmanWorkstation\netprovider
This key has several values. Double-click the "Devicename" value and change the case of the first letter in the data to uppercase. You'll be changing
"\device\LanmanRedirector" to "\Device\LanmanRedirector"
Why does this make a difference? Whenever there is a file that could be a POSIX file, Windows NT needs to open the file in a POSIX-compatible way. This means that the path and filename must match exactly with respect to case-sensitivity.
However, the case of "device" is wrong, so the operating system refuses to open the file when POSIX semantics are requested—it returns ERROR_FILE_NOT_FOUND. The application must open the file a second time, this time specifying not to use POSIX semantics. Thus, the performance penalty occurs.
The case of the Devicename value has been changed to uppercase in Windows NT 3.51.