The First Generation of DAFS

Network Appliance (NetApp) has emerged as the first company out of the box with technology based on the new Direct Access File System (DAFS). Last week, the company announced DAFS Database Accelerator, a high-performance extension of its database-storage solutions for IBM DB2, Oracle8i and Oracle9i, and Sybase 12.5 database environments. NetApp's announcement marks the first of what should be a succession of announcements about new storage products designed to enhance database performance.

DAFS is a file-access protocol designed to take advantage of standard memory-to-memory interconnect technologies such as the Virtual Interface (VI) architecture, InfiniBand, and iWarp. DAFS should improve the performance, scalability, and reliability of Internet, enterprisewide, and intensive I/O applications in clustered data-center applications. Led by NetApp and Intel, the DAFS Collaborative is a joint effort of 87 companies that have been developing the protocol for more than a year. With the release of specification 1.0, the DAFS Collaborative reorganized to form the DAFS Implementers Forum under the auspices of the Storage Networking Industry Association (SNIA).

The concept behind DAFS is simple. The protocol lets applications access network interface hardware without OS intervention. Applications can also carry out bulk-data transfers directly to or from application buffers with minimal CPU overhead, which frees up application CPU cycles for application processing and provides high-performance, low-latency shared-file access between application servers and storage systems. The bottom line: DAFS promises to provide a higher-performance, lower-cost application and storage infrastructure.

In its own tests, NetApp found that the DAFS Database Accelerator reduced CPU cycles by as much as 66 percent compared with Direct Attached Storage (DAS) with a volume manager. The accelerator even absorbed fewer CPU cycles than raw access to DAS. In short, the DAFS Database Accelerator provided better performance than a raw-access configuration, yet the accelerator has the same ease of management as a system with volume management. NetApp executives claim that the results compare favorably with Fibre Channel implementations.

To measure overall system-performance increase, the company conducted Transaction Processing Performance Council (TPC)-C benchmark tests with a configuration that included a Fujitsu Siemens 16 CPU server, NetApp F820 files, the DAFS Database Accelerator, and a Sybase ASE database. The TPC-C benchmark is a primary, online transaction processing (OLTP) benchmark that simulates an environment in which users execute different transactions against a database.

The system returned results of 112,286.46 transactions per minute (tpm) at $13.44 per minute. On a raw performance comparison, those results placed the benchmark configuration in the middle of similar systems, but the results represent the best price and performance for any UNIX system and the best performance per processor for all Sun Microsystems' Solaris systems. The benchmark configuration is as significant as the raw performance numbers. The system ran on a Gigabit Ethernet network and standard RAID storage hardware. Fibre Channel technology is usually standard in such benchmark tests, but NetApp generated these results on what's usually a lower-cost infrastructure.

NetApp officials point out that although its implementation of DAFS used Gigabit Ethernet and the VI architecture, the protocol will be more widely available as InfiniBand-based products emerge in the market. InfiniBand is suited to cluster environments, which need low-latency, high-bandwidth connections to support seamless load balancing, rapid application failover, and parallel database optimizations. Industry observers feel that the InfiniBand architecture provides such fast, cluster-class links that it will ultimately be part of virtually every server and that DAFS is an efficient complement to the InfiniBand architecture.

In any case, the NetApp release is just that—a first release. Although the release runs transparently with the major database environments, future releases will have even tighter integration with the database servers. As the integration improves, the performance that the NetApp implementation provides can more than double, according to company officials.

Nobody expects DAFS technology to "take over the world" immediately. Databases will continue to run in heterogeneous environments requiring several different access methods. Nonetheless, over the next year, DAFS should emerge as an important alternative for enterprise-level database applications.

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