First DAFS product debuts

By Lisa Coleman

Two years after launching the Direct Access File System (DAFS) initiative, Network Appliance is rolling out the first DAFS product, which will accelerate performance for IBM DB2, Oracle 8i and 9i, and Sybase database environments running on Network Appliance filers.

The improvement to transaction processing performance using DAFS and network-attached storage (NAS) may rival iSCSI, according to one analyst. "The big knock on NAS has been the performance, primarily in transaction processing. But now you have a whole new ballgame," says Randy Kerns, senior partner at the Evaluator Group consulting and research firm.

The DAFS Database Accelerator 1.0 uses Virtual Interface (VI) technology over a Gigabit Ethernet interconnect to support larger data workloads on existing hardware.

The accelerator is available with Network Appliance's F800-Series filers running the proprietary DataOnTap 6.2 software, which now supports the DAFS protocol. However, users must purchase a DAFS protocol license, and the filer must be equipped with an Emulex GN9000/VI host bus adapter (HBA). The accelerator will not work with NetApp's F700 Series. A database server-attach kit will also be available. It will include an Emulex GN9000/VI HBA and DAFS accelerator driver software.

DAFS is a file-access protocol based on NFS Version 4. The protocol is designed specifically for high-performance file sharing in data-center environments and uses a memory-to-memory I/O architecture and runs on Fibre Channel, Gigabit Ethernet, and InfiniBand.

The accelerator derives its speed from reduced CPU overhead on the database server, because VI is implemented in the HBA, according to David Dale, marketing manager at Network Appliance and co-chair of the DAFS Collaborative. "The goal is to leapfrog direct-attached or SAN-attached performance for high-intensity online transaction processing [OLTP] workloads," explains Dale.

Network Appliance claims it measured 70ms CPU overhead per operation on a database server using the DAFS accelerator. The test compared the DAFS implementation to the following systems: direct-attached storage (DAS) using a volume manager (113ms), DAS with a local file system (89ms), and raw access to DAS (76ms).

The test used a 4-CPU Sun E3000 running Solaris. The OLTP workload included 66% reads and 34% writes using 4KB transfers and asynchronous I/O. Dale credits Gigabit Ethernet and the Emulex HBAs for the overhead reduction in the DAFS system and also cites performance of 325MBps and up to 30,000 I/Os per second, out of a single filer.

The tests were performed in NetApp's labs using a test similar to the Transaction Processing Performance Council (TPC-C) instruction mix.

"Their tests don't necessarily tell you about overall performance," says Kerns, "but they tell you about the instantaneous response time. Those are probably fairly accurate numbers, but that doesn't necessarily tell you how it's going to work in your environment. But those are stunning numbers."

The company also performed a TPC-C test to measure performance and price/performance. The test ran on a 16-CPU Fujitsu Siemens server, Network Appliance's F820 filers, a Sybase database, and the DAFS accelerator. The total amount of storage was about 8TB in a RAID 4 configuration. The test results yielded 112,286.46 transactions per minute (tpmC) at $13.44 per tpmC.

The DAFS test implementation did not require any changes to the application software. In future implementations of DAFS, however, application modifications will be necessary—which DAFS opponents have criticized the protocol for requiring. "The disadvantage is that you need changes in the application, but the advantage is that you get huge performance boosts," says Dale.

Founded by Network Appliance and Intel, the DAFS Collaborative includes 87 companies. The collaborative published DAFS specification v1.0 and API specification v1.0 in September and November 2001, respectively.

After completing the specifications, the collaborative disbanded into three separate initiatives. One is pursuing the DAFS specification's progress through the IETF standards body, and another group is part of the DAFS Implementer's Forum within the Storage Networking Industry Association (SNIA).

The third group is participating in the Direct Access Transport (DAT) collaborative, which is a spin-off of the DAFS transport working group. The DAT collaborative is writing a set of transport- independent, platform-independent APIs that exploit the remote direct memory access (RDMA) capabilities of InfiniBand, the VI architecture, and iWARP-RDMA over 10 Gigabit Ethernet.

"InfiniBand's native transfer is also VI," says Kerns, "so DAFS may represent the future when we get InfiniBand-based servers and InfiniBand-based storage."

This article was originally published on May 01, 2002