We have a case where we're accessing a RAID array (drive E:) on a Windows Server 2008 SP2 x86 box. (Recently installed, nothing other than SQL Server 2005 on the server.)
In one scenario, when directly accessing it (E:\folder\file.xxx) we get 45MBps throughput to a video file.
If we access the same file on the same array, but through UNC path (\server\folder\file.xxx) we get about 23MBps throughput with the exact same test.
Obviously the second test is going through more layers of the stack, but that's a major performance hit.
What tuning should we be looking at for making the UNC path be closer in performance to the direct access case?
(corrected: it is CIFS not SMB, but generalized title to 'file share'.)
(additional info: this happens during the read from a single file, not an issue across multiple connections. the file is on the local machine, but exposed via file share. so client and file server are both same Windows 2008 server.)