max_async_ports(5)max_async_ports(5)NAMEmax_async_ports - maximum number of asynchronous disk ports that can be
open at any time
VALUES
Failsafe
Default
Allowed values
Recommended values
There is no recommended value for this tunable. The number of pro‐
cesses 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-per‐
formance 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.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect immediately if the new value is
allowed; otherwise the change takes effect at next boot. Increases
within the allowed range are always accepted immediately. Decreases in
the value may take effect immediately, or may be deferred until next
boot depending on the current number of ports in use or the maximum
number of ports ever used.
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. Set‐
ting a higher value would result in the driver using slightly more ker‐
nel memory. Other kernel components which may need kernel memory could
suffer. However, the amount of memory reserved for each port is low.
Only when a new port is actually issued does any significant amount of
memory get consumed.
When Should the Value of This Tunable Be Lowered?
There should be no real need to lower the value of the tunable. How‐
ever, if many processes are opening the async driver and allocating
ports, then lowering the value will put a cap on the maximum number of
ports that can be allocated and will put a cap on the maximum amount of
memory that the driver may allocate.
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 num‐
ber 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 parame‐
ter 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 val‐
ues. For information about the effects of installation on tunable val‐
ues, consult the documentation for the kernel software being installed.
For information about optional kernel software that was factory
installed on your system, see at
AUTHOR
was developed by HP.
Tunable Kernel Parameters max_async_ports(5)