VERITAS File System 4.1 Administrator's Guide

The VERITAS File System
Enhanced I/O Performance
Chapter 1 27
Enhanced I/O Performance
VxFS provides enhanced I/O performance by applying an aggressive I/O clustering policy,
integrating with VxVM, and allowing application specific parameters to be set on a per-file
system basis.
Enhanced I/O Clustering
I/O clustering is a technique of grouping multiple I/O operations together for improved
performance. VxFS I/O policies provide more aggressive clustering processes than other file
systems and offer higher I/O throughput when using large files; the resulting performance is
comparable to that provided by raw disk.
VxVM Integration
VxFS interfaces with VxVM to determine the I/O characteristics of the underlying volume and
perform I/O accordingly. VxFS also uses this information when using mkfs to perform proper
allocation unit alignments for efficient I/O operations from the kernel.
As part of VxFS/VxVM integration, VxVM exports a set of I/O parameters to achieve better
I/O performance. This interface can enhance performance for different volume configurations
such as RAID-5, striped, and mirrored volumes. Full stripe writes are important in a RAID-5
volume for strong I/O performance. VxFS uses these parameters to issue appropriate I/O
requests to VxVM.
Application-Specific Parameters
You can also set application specific parameters on a per-file system basis to improve I/O
performance.
• Discovered Direct I/O
All sizes above this value would be performed as direct I/O.
• Maximum Direct I/O Size
This value defines the maximum size of a single direct I/O.
For a discussion on VxVM integration and performance benefits, refer to “VxFS Performance:
Creating, Mounting, and Tuning File Systems” on page 37, “Application Interface” on page 75,
and the vxtunefs (1M) and tunefstab (1M) manual pages.