Understanding the DAFS protocol

DAFS protocol overview

The DAFS protocol defines a set of file access and management operations similar to Network File System (NFSv4), but optimized for the local file-sharing and clustered environments. A local file-sharing environment is one that is geographically constrained (one or a few machine rooms) with mostly homogeneous clients. It is managed from a single administrative control point and focused on supporting high-performance applications. An example is a data center.

How DAFS optimizes I/O performance

The DAFS protocol provides high-performance file input/output (I/O), improved CPU utilization, and low networking overhead by transporting data over a direct access transport (DAT) interface. DAT is an interface to memory-to-memory networks.

Note
This version of Data ONTAP supports virtual interface over Gigabit Ethernet (VI/IP) memory-to-memory networking only.

The DAFS protocol optimizes application throughput with streamlined messaging composition and transport. Flow control enables multiple application servers to access a single NetApp filer without congestion.

About direct access transport (DAT)

DAT describes a networking infrastructure that provides the following capabilities:

Remote Direct Memory Access (RDMA)
RDMA directly transfers data between application memory and the memory of a remote machine without file system switches or operating system calls.
Direct access to the network interface
Application programs can initiate data transfer operations directly to a network interface card (NIC) without operating system intervention.

DAT improves data transfer by bypassing the operating system and moving data directly between application buffers and NIC hardware memory. As a result, DAT reduces the overall number of copies, operating system calls, and file system switches required to move data. DAT also reduces networking overhead because the operating system does not perform data fragmentation or reassembly. The DAT-compliant NIC manages data delivery to and from the network, so protocol processing is performed at the hardware level.