HP-UX Reference (11i v2 03/08) - 1M System Administration Commands N-Z (vol 4)

v
vxtunefs(1M) vxtunefs(1M)
value to determine how much data to read ahead. The default value is 64K.
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 and write_pref_io
to determine when to
do flush behind on writes. The default value for
write_nstream is 1.
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.
write_throttle
When data is written to a file through buffered writes, the file system updates only the in-memory
image of the file, creating what are referred to as dirty buffers. Dirty buffers are cleaned when the
the file system later writes the data in these buffers to disk. (Note that data can be lost if the sys-
tem crashes before dirty buffers are written to disk.)
Newer model computer systems typically have more memory. The more physical memory a system
has, the more dirty buffers the file system can generate before having to write the buffers to disk to
free up memory. So more dirty buffers can potentially lead to longer return times for operations
that write dirty buffers to disk such as
sync and fsync. If your system has a combination of a
slow storage device and a large amount of memory, the sync operations may take long enough to
complete that it gives the appearance of a hung system.
If your system is exhibiting this behavior, you can change the value of
write_throttle
.
write_throttle lets you lower the number of dirty buffers per file that the file system will gen-
erate before writing them to disk. After the number of dirty buffers for a file reaches the
write_throttle threshold, the file system starts flushing buffers to disk even if free memory is
still available. Depending on the speed of the storage device, user write performance may suffer,
but the number of dirty buffers is limited, so sync operations will complete much faster.
The default value of write_throttle is zero. The default value places no limit on the number of dirty
buffers per file. This typically generates a large number of dirty buffers, but maintains fast writes.
If
write_throttle is non-zero, VxFS limits the number of dirty buffers per file to
write_throttle buffers In some cases,
write_throttle may delay write requests. For
example, lowering the value of
write_throttle
may increase the file disk queue to the
max_diskq value, delaying user writes until the disk queue decreases. So unless the system has a
combination of large physical memory and slow storage devices, it is advisable not to change the
value of write_throttle
.
FILES
/etc/vx/tunefstab
VxFS file system tuning parameters table.
SEE ALSO
mkfs_vxfs(1M), mount(1M), mount_vxfs(1M), sync(2), tunefstab(4), vxfsio(7).
VERITAS File System Administrator’s Guide
VERITAS Volume Manager Administrator’s Guide
Section 1M−−912 Hewlett-Packard Company − 4 − HP-UX 11i Version 2: August 2003