Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

VxFS Performance: Creating, Mounting, and Tuning File Systems
I/O Tuning
Chapter 250
max_seqio_extent_
size
Increases or decreases the maximum size of an extent. When the file
system is following its default allocation policy for sequential writes
to a file, it allocates an initial extent which is large enough for the
first write to the file. When additional extents are allocated, they are
progressively larger (the algorithm tries to double the size of the file
with each new extent) so each extent can hold several writes worth of
data. This is done to reduce the total number of extents in
anticipation of continued sequential writes. When the file stops being
written, any unused space is freed for other files to use. Normally this
allocation stops increasing the size of extents at 2048 blocks which
prevents one file from holding too much unused space.
max_seqio_extent_size is measured in file system blocks.
qio_cache_enable 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 will perform
aggressive read-ahead on the files.
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.