JFS Tuning and Performance

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Executive summary
File system performance is critical to overall system performance. While memory latencies are
measured in nanoseconds, I/O latencies are measured in milliseconds. In order to maximize the
performance of your systems, the file system must be as fast as possible by performing efficient I/O,
eliminating unnecessary I/O, and reducing file system overhead.
In the past several years many changes have been made to the Veritas File System (VxFS) as well as
HP-UX. This paper is based on VxFS 3.5 and includes information on VxFS through version 5.0.1,
currently available on HP-UX 11i v3 (11.31). Recent key changes mentioned in this paper include:
 page-based Unified File Cache introduced in HP-UX 11i v3
 improved performance for large directories in VxFS 5.0
 patches needed for read ahead in HP-UX 11i v3
 changes to the write flush behind policies in HP-UX 11i v3
 new read flush behind feature in HP-UX 11i v3
 changes in direct I/O alignment in VxFS 5.0 on HP-UX 11i v3
 concurrent I/O included with OnlineJFS license with VxFS 5.0.1
 Oracle Disk Manager (ODM) feature
Target audience: This white paper is intended for HP-UX administrators that are familiar with
configuring file systems on HP-UX.
Introduction
Beginning with HP-UX 10.0, Hewlett-Packard began providing a Journaled File System (JFS) from
Veritas Software Corporation (now part of Symantec) known as the Veritas File System (VxFS). You no
longer need to be concerned with performance attributes such as cylinders, tracks, and rotational
delays. The speed of storage devices have increased dramatically and computer systems continue to
have more memory available to them. Applications are becoming more complex, accessing large
amounts of data in many different ways.
In order to maximize performance with VxFS file systems, you need to understand the various
attributes of the file system, and which attributes can be changed to best suit how the application
accesses the data.
Many factors need to be considered when tuning your VxFS file systems for optimal performance. The
answer to the question “How should I tune my file system for maximum performance?” is “It depends”.
Understanding some of the key features of VxFS and knowing how the applications access data are
keys to deciding how to best tune the file systems.
The following topics are covered in this paper:
 Understanding VxFS
 Understanding your application
 Data access methods
 Creating your file system
 Mount options
 Dynamic File system tunables
 System wide tunables
 VxFS ioctl() options