Since Apple released Mac OS X (10), no longer were users limited to connecting to file servers sharing via AFP, but they were opened to the Windows world of SMB. However, over the years, Macintosh computers have been plagued with problems connecting to Windows shares. A simply query of Google will demonstrate this. The underlying problem is the often buggy SAMBA subsystem which processes SMB shares. Everything from authentication problems to memory leaks, it provides “best effort” SMB connectivity.
Recently while performing some tests, we have confirmed that Mac to Mac or Mac to Unix or Mac to PC, whenever AFP is available, file transfers appear to be more reliable and occur faster. Not faster than a Windows to Windows SMB transfer, but rather faster when compared to a Mac to anything transfer using SMB versus AFP.
So if your SMB transfers for your Mac seem to drag, consider switching to AFP, which is available on Mac, Windows and Unix servers.