NAME
max_async_ports — maximum number of asynchronous disk ports that can be open at any time
VALUES
Allowed values
1 - 4194304
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.
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.
Setting a higher value would result in the driver using slightly
more kernel 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.
However, 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 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 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
http://docs.hp.com.
AUTHOR
max_async_ports
was developed by HP.
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