VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
I/O Tuning
Chapter 2 65
read_ahead The default for all VxFS read operations is to perform
sequential read ahead. You can specify the read_ahead
cache advisory to implement the VxFS enhanced read
ahead functionality. This allows read aheads to detect more
elaborate patterns (such as increasing or decreasing read
offsets or multithreaded file accesses) in addition to simple
sequential reads. You can specify the following values for
read_ahead:
0—Disables read ahead functionality
1—Retains traditional sequential read ahead behavior
2—Enables enhanced read ahead for all reads
The default is 1—VxFS detects only sequential patterns.
read_ahead detects patterns on a per-thread basis, up to a
maximum determined by vx_era_nthreads parameter. The
default number of threads is 5, but you can change the
default value by setting the vx_era_nthreads parameter in
the /etc/system configuration file.