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> The Linux client is asking for SMB1 and using 1MB write sizes. > > The Windows client is using SMB2 and *NOT ASKING FOR LEASES*. > > This is why the performance is terrible. Because the file > as no lease, the Windows redirector must pass every single > WriteFile() system call onto the wire, no matter how small > the size. > > If you can get the Windows SMB2 client

...any redirector caching by using FILE_FLAG_WRITE_THROUGH on the CreateFile() Win32 call. If you can do the equivalent of strace on Windows (I don't know how) you might be able to confirm that and ask the app developer to stop doing that. https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858(v=vs.85).aspx FILE_FLAG_WRITE_THROUGH 0x80000000 Write operations will not go through any intermediate cache, they will go directly to disk. For additional information, see the Caching Behavior section of this topic.