VI: Enabling High-Performance Data Access - Industry Trend or Event - Column

Computer Technology Review, Feb, 2001 by Mike Dutch, Marc Shelley

This is the fourth in a series of columns authored by members of the DAFS Collaborative, an industry group formed to create a protocol specification for direct, memory-to-memory data networking.

The Virtual Interface (VI) Architecture, released in 1997 by Compaq, Intel, and Microsoft, is a specification for a high-performance networking interface which dramatically reduces the overhead of traditional network architectures. To accomplish this, VI defines mechanisms which allow applications to access VI network adapters without operating system intervention and carry out bulk data transfers directly to or from application buffers.

First generation VI implementations typically featured parallel database applications running in clustered environments. The second generation VI Network Adapters discussed in this article enables a new generation of applications deployed in high-performance standards-based clustered environments.

What Is A Virtual Interface?

Several components are brought together to create a 'Virtual Interface', as shown in Figure 1.

A Virtual Interface is created by a VI "Provider" (VI Network Adapter) when requested to do so by a VI "Consumer" (application).

A Virtual Interface consists of a Send Queue and a Receive Queue, which hold Descriptors of data movement requests. Descriptors contain all of the information the VI NIC needs to process the requests. However, data transfer does not occur until VI pairs are connected. A connected pair of Virtual Interfaces forms a bi-directional, memory-to-memory virtual circuit. Doorbells are used to notify a VI NIC that work (new Descriptor) has been placed on one of the Work Queues. A Completion Queue holds information about completed Descriptors from multiple Work Queues.

A VI Provider initiates a Virtual Interface using a VI NIC and a VI Kernel Agent. The VI Kernel Agent is a device driver for the VI NIC that registers application memory and manages VIs. The VI Consumer, consisting of an application program, communications facility and a VI User Agent, communicates using a VI. The VI User Agent is the software that abstracts the underlying VI NIC in accordance with an interface defined by the Operating System communication facility. An implementation of the VI User Agent is called a Virtual Interface Provider Library (VIPL).

VI-Enabled Applications Provide Improved Use Of Resources

Parallel databases, including Oracle Parallel Server, IBM DB2 UDB EEE, and Microsoft SQL Server 2000 were early adopters of VI, exploiting the benefits of direct memory access. Native support for VI allows these applications to place data directly on the wire without copying data to kernel buffers. VI has enabled these applications to achieve benchmark results previously obtained only on mainframe class systems.

Oracle Net8 (and its predecessor for Oracle7 called SQL*Net) was another early adopter, using VI to speed network communications. Although focused initially on providing low-latency message passing for distributed applications, VI has garnered growing acceptance as a mechanism to accelerate data access. One example is Computer Associates International's use of VI in its ARCserve 2000 Workgroup/Advanced Edition Backup Agent for Microsoft SQL Server, doubling performance over its 100BaseT Ethernet offering.

VI Network Adapters

Leading providers of VI network adapters include Giganet and Troika Networks.

Giganet's cLAN solutions have been enabling high performance VI-based data center networks since 1998. The cLAN product suite includes host adapters and cluster switches supporting server farm networks in Windows and Linux environments. Giganet customers have built server farms ranging in size from two nodes to greater than 100 nodes, deployed in business critical environments such as e-commerce, high availability computing, data warehousing, parallel databases, and scientific and technical computing.

Troika pioneered the notion of simultaneously running multiple protocols over a common wire transport. The Troika Zentai Controller supports industry standard networking and storage protocols (FC-VI, IPFC, FCP-SCSI) over networks based on the Fibre Channel standard. Coupled with management software (employing an industry standard HBA API) and unique dynamic multipathing capabilities, the Zentai Controller has enabled Internet data centers to consolidate their storage and cluster networks.

Next generation network adapters will leverage VI to embrace other networking technologies, including Gigabit Ethernet and InfiniBand.

Giganet has recently introduced a second product family called VI/IP By incorporating both VI and TCP/IP into a single architecture, Giganet's new VI/IP products will combine the speed and efficiency of VI with the standard structure of the IP transport. Supported on existing Gigabit Ethernet infrastructures, Giganet's VI/IP products will bring the power and benefits of VI to an Ethernet standard environment.

InfiniBand defines a switched communications fabric for connecting multiple end nodes with high bandwidth and low latency in a protected, remotely managed environment. It defines the host behavior (verbs) and memory operation such that the channel adapter can be located as close to the memory complex as possible. The InfiniBand point-to-point switched fabric supports reliable messaging (send/receive) and memory manipulation (remote DMA) without software in the data path, providing enhancements to VI.