VERITAS File System 4.1 Administrator's Guide

VxFS Performance: Creating, Mounting, and Tuning File Systems
I/O Tuning
Chapter 2 59
Tunable VxFS I/O Parameters
read_pref_io The preferred read request size. The file system uses this in
conjunction with the read_nstream value to determine how
much data to read ahead. The default value is 64K.
write_pref_io 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.
read_nstream 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.
write_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.
discovered_direct
_iosz
Any file I/O requests larger than the
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.