CIFS File Sharing

On computer networks that have Windows, UNIX, Linux, and many other operating systems the SMB or Server Message Block Protocol is widely used for file transfers, print communications, backup, and replication. SMB, also known as the Common Internet File System or CIFS underpins a wide variety of important services that all networks need to run properly. Windows uses CIFS for a variety of server and workstation services, UNIX uses it for the file sharing service Samba, Windows “Network Neighborhood” discovery processes run NetBIOS transport with SMB, and many familiar functions are based on this transport type. The word “small” in the name SMB speaks to some of the issues one encounters when SMB and CIFS traffic flows over a WAN connection. SMB/CIFS were designed to run on LANs and were not optimized for low bandwidth, high latency broadband WAN connections. Various factors such as the small 64K block size, excessive reliance on small control message packets (which makes this protocol “chatty”), SMB signing, and poor connection persistence are characteristics that make CIFS traffic perform very poorly on a WAN.

aCelera CIFS Application Blueprint

The aCelera solution is deployed at both ends of a WAN connection can greatly speed up CIFS traffic. Using the CIFS Application Blueprint, CIFS traffic is identified, parsed into objects, and then stored for later use at both ends of the connection. aCelera recognizes traffic it has previously seen and only sends reference IDs across the wire to recreate the file using data stored remotely. This approach then only requires that the pieces of a file that have changed are then sent across the wire, a form of optimization referred to as file level differencing.

The Blueprint uses a system for status information caching which tracks associations between file and directory paths and open file descriptors. A range of status information can be cached. This enables aCelera to autonomously respond to client status requests without requiring traffic be sent over the WAN or to a server. Because such status requests account for nearly 50% of all CIFS requests, this results in big improvements to response times for the user.

Using a technique called Intelligent Read Ahead aCelera can overcome WAN latency by intelligently and proactively creating READ requests to the server. Without waiting for a response for each request to complete, these forward READs act to keep the file in transmission over the WAN. SMB file transfers therefore are greatly speeded up using Intelligent Read Ahead.

The last part of the aCelera CIFS Application Blueprint addresses the chattiness problem that CIFS messaging presents. Techniques such as spoofing server responses provide the appropriate messaging when a file closes, at disconnect or logoff, and for other client requests without the SMB message having to travel across the WAN link, an answer generated, and a response returned.

Shown in the accompanying figure is the results obtained by passing a 1 MB Excel file in XLS format and a 10 MB PowerPoint slide presentation across a WAN connection. That WAN connection’s throughput was set at 1 Mb/s with a 200 msec latency. This experiment shows that both of these CIFS files are greatly accelerated by the aCelera. In the case of the Excel file the acceleration factor was 20X with a reduction in response time of 95%. For the PowerPoint file the reduction was even better, with an acceleration factor of 100X and a reduction of response time of 99%.