HP-UX Reference (11i v2 04/09) - 5 Miscellaneous Topics (vol 9)

m
max_async_ports(5) max_async_ports(5)
(Tunable Kernel Parameters)
NAME
max_async_ports - maximum number of asynchronous disk ports that can be open at any time
VALUES
Failsafe
1
Default
50
Allowed values
1 - 4294967295 (2ˆ64 - 1) (limited by available physical memory)
Recommended values
There is no recommended value for this tunable. The number of processes that will be accessing the
driver simultaneously can be used as a guideline to set a value.
DESCRIPTION
The asynchronous disk driver provides an interface to execute high-performance I/O to the raw disk.
Instead of reading or writing directly to the raw disk, a process writes requests to the asynchronous
driver which then makes appropriate calls to the disk driver.
Every process that opens the asynchronous disk driver is assigned a port. The driver uses the port to
keep track of I/O and other internal resources for that process. The number of opens to the asynchronous
disk driver is limited by the number of available ports.
The value of this tunable should not be set greater than the value of nproc since such a value cannot not
be used.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
When Should the Value of This Tunable Be Raised?
When the number of processes opening the driver needs to be more than the current value of the tunable.
What Are the Side Effects of Raising the Value of This Tunable?
The resources for the port are allocated from the kernel memory. Setting a higher value would result in
the driver using more kernel memory. Other kernel components which may need kernel memory could
suffer.
When Should the Value of This Tunable Be Lowered?
When the system is low on physical memory and there are not as many opens necessary to access the
driver.
What Are the Side Effects of Lowering the Value of This Tunable?
The number of simultaneous opens are limited by this tunable. This may impact the performance of
applications that need to have a higher number of processes accessing the driver.
What Other Tunables Should Be Changed at the Same Time?
None.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its
meaning changed in future releases of HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-
ter values. After installation, some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable values, consult the documentation for
the kernel software being installed. For information about optional kernel software that was factory
installed on your system, see HP-UX Release Notes at
http://docs.hp.com.
Section 5−−184 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: September 2004