Veritas File System 5.0 Administrator's Guide (September 2006)

Table 2-1
Tunable VxFS I/O parameters (continued)
DescriptionParameter
Enables or disables caching on Quick I/O files. The default
behavior is to disable caching. To enable caching, set
qio_cache_enable to 1. On systems with large
memories, the database cannot always use all of the
memory as a cache. By enabling file system caching as a
second level cache, performance may be improved. If the
database is performing sequential scans of tables, the
scans may run faster by enabling file system caching so
the file system performs aggressive read-ahead on the
files.
qio_cache_enable
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.
read_ahead
53VxFS performance: creating, mounting, and tuning file systems
Tuning I/O