VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 1

The VERITAS File System

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 17, “Application Interface” on page 43, and the vxtunefs (1M)

and tunefstab (1M) manual pages.