Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

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

Enables or disables thin friendly allocations.

Specifying a value of 1 enables thin friendly

allocations, while specifying a value of 0 disables thin

friendly allocations. The default value is 1 for

thinrclm volumes, and 0 for all other volume types.

You must turn on delicache_enable before you

can activate this feature.

thin_friendly_alloc

VxFS performance: creating, mounting, and tuning file systems

Tuning I/O