File Systems Tunable Parameters

Many of the HP-UX File Systems tunable parameters are now dynamic tunables (their value can be modified without the need to reboot the system). Several default values and allowed values for File Systems tunables have also been modified for performance, usability, and/or system availability reasons.

Summary of Change

HP-UX File Systems now has 13 dynamic tunable parameters available in HP-UX 11i v2. Their values can be modified dynamically using the tunables infrastructure interfaces (e.g., kctune(1M), kcweb(1M)^[1], settune(2)).

The following File Systems tunables were static in previous HP-UX releases, and have been converted to dynamic tunables in HP-UX 11i v2. In addition to making these tunables dynamic, some of the default and/or allowed values have been modified. See the manpages for details:

The following are new File Systems dynamic tunables:

fs_symlinks(5) - Maximum number of symbolic links used to resolve a path name
aio_proc_threads(5) - Maximum number of process threads allowed in AIO pool
aio_monitor_run_sec(5) - Frequency of AIO thread pool monitor execution (in seconds)
aio_proc_thread_pct(5) - Percentage of all process threads allowed in AIO pool
aio_req_per_thread(5) - Desirable ratio between number of pending AIO requests and servicing threads

The maxfiles_lim(5) tunable has been dynamic in previous HP-UX releases, but its default and allowed values have been modified. See manpage for details.

The following file systems tunables remain static (system reboot is required when modified), but have been enhanced with new default and/or allowed values. See manpages for details:

Tunable parameters related to the static buffer cache that existed in previous HP-UX releases are now considered obsolete. The recommended way to obtain a fixed size buffer caches is to set the value or tunable dbc_min_pct equal to the value of tunable dbc_max_pct.

Impact

The new default values were selected to improve performance in the majority of system environments, but may not be suitable or optimum for all systems and environments. By making the tunables dynamic, the values of the tunables can now be modified while maintaining system availability.

System update scripts take new tunables restrictions into consideration, adjusting the tunables values to new allowed values if necessary.

Compatibility

System update scripts take new tunables restrictions into consideration, adjusting the tunables values to new allowed values if necessary.

For the MAXSYMLINKS literal, and the tunables nbuf, bufpages and bufcache_max_pct, compatibility will be maintained through HP-UX 11i v2, but obsolescence is planned for the next release. See the following obsolescence section.

Performance

The new default values were selected to improve performance in the majority of system environments, but may not be suitable or optimum for all systems and environments.

Documentation

The following manpages have changed:

The following manpages are new:

Tunables manpages (section 5) can be found at http://www.docs.hp.com.

For general HP-UX Tunables Infrastructure documentation, see the HP-UX 11i v2.0 Driver Development Guide (DDG), available at http://h21007.www2.hp.com/dspp/tech/tech_TechSoftwareDetailPage_IDX/1,1703,5441,00.html.

Obsolescence

The following has been deprecated in HP-UX 11i v2, and will be obsolete in post-HP-UX 11i v2 releases:

The MAXSYMLINKS literal traditionally included in the <sys/param.h> header is being deprecated in HP-UX 11i v2 and should not be used by applications. MAXSYMLINKS was defined as the maximum number of symbolic links that may be expanded in a path name.
This limit (number of symbolic links that may be expanded in a path name) is now a tunable parameter: fs_symlinks. The interfaces provided by the tunable infrastructure should be used to obtain the value of fs_symlinks. At the application level, for example, use the gettune(2) or kctune(1M) interfaces.
Applications using the MAXSYMLINKS literal may not be consistent with the kernel. The MAXSYMLINKS literal will be removed from <sys/param.h> in post-HP-UX 11i v2 releases.
All tunables associated to the buffer cache (nbuf, bufpages, bufcache_max_pct, dbc_min_pct, and dbc_max_pct) are still supported through HP-UX 11i v2, but will be obsolete in future HP-UX releases. The dbc_min_pct and dbc_max_pct tunables will be replaced with new dynamic tunables that will control the amount of memory to be used for file caching in general (for caching file I/O data and metadata).

^[1]For more information about kcweb, see “HP-UX Kernel Configuration”.