VERITAS File System 3.5 (HP OnlineJFS/JFS 3.5) Administrator's Guide (August 2003)

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 29, “Application Interface” on page 55, and the vxtunefs (1M)

and tunefstab (1M) manual pages.