default_disk_ir man page on HP-UX

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default_disk_ir(5)					    default_disk_ir(5)

       default_disk_ir - enable and disable use of device's write cache in the
       SCSI subsystem (OBSOLETE)

   Allowed values
   Recommended values
       Note: This tunable is obsolete.	 HP  no	 longer	 allows	 enabling,  by
       default,	 write	cache for all direct access devices on the system.  It
       is still possible to enable write cache for a specific  device  through
       the command.  See scsictl(1M).

       This tunable enables (1) or disables (0) the Immediate Reporting behav‐
       ior of the SCSI subsystem, also known  as  Write	 Cache	Enable	(WCE).
       With  Immediate	Reporting  enabled,  disk drives that have data caches
       return from a system call, including  raw  writes,  when	 the  data  is
       cached,	rather	than returning after the data is written to the media.
       This sometimes improves write  performance  especially  for  sequential

       Cached  data  can  be  lost  if	a device power failure or reset occurs
       before the device writes the cached data to  media.  Because  of	 these
       risks, the recommended value for this parameter on servers is Immediate
       Reporting disabled (0).

       Although not an option to the mount command, this tunable  has  a  pro‐
       found  effect upon filesystem and raw disk performance and, conversely,
       data integrity when system resets occur.	  This	tunable	 also  affects
       delayed-write versus write-through-filesystem behavior.

   Who Is Expected to Change This Tunable?

   Restrictions on Changing
       Changes	to  this  tunable  will	 take  effect when the device is first

   When Should the Tunable Be Turned On?
       When a third party application vendor recommends it.  For  normal  use,
       HP strongly recommends you don't enable this tunable.

   What Are the Side Effects of Turning the Tunable On?
       Since enabling this tunable circumvents the protections provided by LVM
       or RAID, there is a strong risk of filesystem corruption and data  loss
       in case of a device power failure or reset.

   When Should the Tunable Be Turned Off?
       HP recommends you always disable this tunable.  This is especially true
       if you don't want to take the risk of filesystem	 corruption  and  data
       loss in case of a device power failure or reset.

   What Are the Side Effects of Turning the Tunable Off?
       This might reduce the performance of disk write (not read) access while
       eliminating the risk of filesystem corruption and data loss in case  of
       a device power failure or reset.

   What Other Tunables Should Be Changed at the Same Time?

       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter has been obsoleted for HP-UX 11i Version 3.

       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

       was developed by HP.

       write(2), scsi(7).

OBSOLETE		   Kernel Tunable Parameter	    default_disk_ir(5)

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