Veritas™ File System 5.0.1 Administrator's Guide

Table 2-1
Tunable VxFS I/O parameters (continued)
DescriptionParameter
The preferred write request size. The file system uses this
in conjunction with the write_nstream value to
determine how to do flush behind on writes. The default
value is 64K.
write_pref_io
The number of parallel read requests of size
read_pref_io to have outstanding at one time. The file
system uses the product of read_nstream multiplied by
read_pref_io to determine its read ahead size. The
default value for read_nstream is 1.
read_nstream
The number of parallel write requests of size
write_pref_io to have outstanding at one time. The
file system uses the product of write_nstream
multiplied by write_pref_io to determine when to do
flush behind on writes. The default value for
write_nstream is 1.
write_nstream
Any file I/O requests larger than
discovered_direct_iosz are handled as discovered
direct I/O. A discovered direct I/O is unbuffered similar
to direct I/O, but it does not require a synchronous commit
of the inode when the file is extended or blocks are
allocated. For larger I/O requests, the CPU time for
copying the data into the page cache and the cost of using
memory to buffer the I/O data becomes more expensive
than the cost of doing the disk I/O. For these I/O requests,
using discovered direct I/O is more efficient than regular
I/O. The default value of this parameter is 256K.
discovered_direct_iosz
53VxFS performance: creating, mounting, and tuning file systems
Tuning I/O