max_async_ports man page on HP-UX

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max_async_ports(5)					    max_async_ports(5)

NAME
       max_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)
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