Protocol advances in Server 2008 R2 and Windows 7
Last time I discussed the (relatively) new SMB 2 protocol supported in Vista, Windows 7, and Server 2008. This protocol update can make communications more efficient between Longhorn operating systems. The question naturally arises whether Server 2008 R2 and Windows 7 improve further on SMB, and the answer is yes. These latest operating systems from Microsoft support SMB version 2.1 (also known as the 2.1 “dialect”). In addition to the performance enhancement features I mentioned already in connection with SMB 2.0, SMB 2.1 supports pipelining, the sending of a request before a previous request has been answered. (Think of this as the “Chris Matthews” mode.) Pipelining is likely to boost performance most noticeably in high-latency connections such as WAN links. On the other end of the spectrum, SMB 2.1’s larger buffer sizes should provide speed gains over faster low-latency connections, for example, in 10-gigabit Ethernet networks. The large buffer sizes are subject to negotiation, with the server controlling the maximum size. Server 2008 R2 defaults to a maximum 1-megabyte MTU (Maximum Transmission Unit), but the protocol specification permits even higher values. Microsoft estimates a 30% to 40% gain versus SMB 2.0 in file transfer speeds in a 10-gig environment with the large MTU feature enabled (which it is by default), assuming a 2-gig file size. Of course the results we see in our systems will depend on factors such as RAM cache availability and disk subsystem speeds. Larger MTU’s permit SMB 2.1 systems to cache larger directories, which will add to the performance gains for directories having more than approximately 500 entries.
