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 2 45
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.