Tunable Kernel Parameters
NAME [Toc] [Back]
max_async_ports - maximum number of asynchronous disk ports that can
be open at any time
VALUES [Toc] [Back]
Default [Toc] [Back]
Allowed values [Toc] [Back]
1 - 4294967295 (2^64 - 1) (limited by available physical memory)
Recommended values [Toc] [Back]
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 [Toc] [Back]
The asynchronous disk driver provides an interface to execute highperformance
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
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?
Restrictions on Changing [Toc] [Back]
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
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Tunable Kernel Parameters
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?
WARNINGS [Toc] [Back]
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 parameter 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
AUTHOR [Toc] [Back]
max_async_ports was developed by HP.
SEE ALSO [Toc] [Back]
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]