sys_attrs_io(5) 						File Formats Manual						   sys_attrs_io(5)

NAME

       sys_attrs_io - io subsystem attributes

DESCRIPTION

       This  reference	page  lists  and  describes attributes for the I/O  (io) kernel subsystem. Refer to the sys_attrs(5) reference page for an
       introduction to the topic of kernel subsystem attributes.

	      Amount of space in megabytes to allocate for the 32-bit scatter-gather DMA window on PCI-based AlphaServers.  This parameter is  set
	      by the TruCluster software.

	      Default value: 0 (MB)

	      Do not modify the value of this attribute unless instructed to do so by support personnel or by patch kit documentation.

	      Number  of  entry  dispatch points supported by the in-memory table for the bdev (block device driver) switch. This table is used to
	      access block device drivers, and must be large enough to accommodate the drivers registered in the bdevsw table in the /usr/sys/sys-
	      tem_name /conf.c file, plus any additional device drivers that will be dynamically loaded.

	      Default value: 200

	      Minimum value: 0

	      Maximum value: INT_MAX

	      If  the  number  of  third-party	block device drivers that will be dynamically loaded to the system plus the number of block device
	      drivers already registered in the system_name /conf.c file exceeds 200, you may want to increase the value of bdevsw_size.

	      A query-only attribute that specifies the media from which the system was booted.

	      Number of buffers either added to or removed from the buffer pool free list. Buffers are allocated as they are needed  in  order	to
	      handle immediate demands; however, they are deallocated carefully to prevent spikes.

	      Default value: 50 buffers

	      Do not modify the default setting for this attribute unless instructed to do so by support personnel or by patch kit instructions.

	      A  threshold  value that determines when more buffers are allocated from the kernel. More buffers are allocated from the kernel when
	      the number of buffers in the pool free list falls  below	this  value.   CAM  reserves  the  number  of  buffers	specified  by  the
	      cam_ccb_low_water attribute  to ensure that the kernel always has enough memory to shut down runaway  processes.

	      Default value: 100 (buffers)

	      Do not modify the default setting for this attribute unless instructed to do so by support personnel or by patch kit instructions.

	      The  base  number  of Common Access Method (CAM) control blocks (ccbs) allocated to the buffer pool free list. One ccb is needed for
	      each outstanding I/O request.  The system will automatically increase the number of ccbs, as necessary for the I/O  load,  but  will
	      not decrease allocation of ccbs below cam_ccb_pool_size.

	      Default value: 200 (ccbs)

	      Minimum value: 100

	      Maximum value: 1000

	      If  the I/O load on your system is consistently very high, increasing the number of ccbs that are always available in memory (rather
	      than starting with a lower number and letting the system dynamically increase it when necessary) may improve  performance.  However,
	      by increasing cam_ccb_pool_size, you prevent the system from using the additional memory for other purposes at times when the number
	      of I/O requests is lower than the number of ccbs. Any performance improvement that results from  a  cam_ccb_pool_size  increase  can
	      occur only if your system's memory size is large enough to support the dedication of additional memory resources to I/O.

	      Decreasing cam_ccb_pool_size to a value below the default is very likely to cause I/O problems and is strongly discouraged.

	      Number  of  entry dispatch points supported by the in-memory table for the cdev (character device driver) switch. This table is used
	      to access character device drivers, and must be large enough to accommodate the drivers  registered  in  the  cdevsw  table  in  the
	      /usr/sys/system_name /conf.c file, plus any additional character device drivers that will be dynamically loaded.

	      Default value: 200 (entry dispatch points)

	      Minimum value: 0

	      Maximum value: INT_MAX

	      If  the  number  of  third-party character device drivers that will be dynamically loaded to the system plus the number of character
	      device drivers already registered in the system_name /conf.c file exceeds 200, you may want to increase the value of cdevsw_size.

	      An on/off switch for internal use only. Do not modify this attribute unless instructed to do so by support personnel or by patch kit
	      instructions.

	      An on/off switch for internal use only. Do not modify this attribute unless instructed to do so by support personnel or by patch kit
	      instructions.

	      An on/off switch for internal use only. Do not modify this attribute unless instructed to do so by support personnel or by patch kit
	      instructions.

	      A value used by developers when debugging subsystem source code.

	      Do not modify the default value of this attribute unless instructed to do so by support personnel or by patch kit documentation.

	      Amount of space in megabytes to allocate for the 64-bit scatter-gather DMA window on PCI-based AlphaServers.

	      Default value: 0 (MB)

	      Do not modify this attribute unless instructed to do so by support personnel or by patch kit documentation.

	      A value that controls the zeroing of scatter-gather mapping entries in the PCI adapter on AS8x00 Alphaservers.

	      Default value: 2

	      Do not modify this attribute unless instructed to do so by support personnel or by patch kit documentation.

	      A value used by developers for debugging subsystem source code.

	      Do not modify this attribute unless instructed to do so by support personnel or by patch kit documentation.

	      The  size,  in  bytes, of an I/O read request used by nondriver kernel code if an ioctl() call fails or returns 0 (zero). (When non-
	      driver kernel code needs to know the maximum size of an I/O read request for a block-I/O device, it issues  an  ioctl  call  to  the
	      driver.)

	      Default value: 65,536 (bytes)

	      Change  the  default  value of this attribute only if a third-party device driver does not use the ioctl call and has a maximum size
	      that is less than the default value (65536 bytes, or 64 kilobytes) in the sysconfigtab file .  (The person writing  the  third-party
	      device driver must provide information, either in documentation or an installation script, on how to change the entry in the syscon-
	      figtab file to the correct value.)

	      The size, in bytes, of an I/O write request used by nondriver kernel code if an ioctl() call fails or returns 0 (zero).  (When  non-
	      driver  kernel  code needs to know the maximum size of an I/O write request for a block-I/O device, it issues an ioctl() call to the
	      driver.)

	      Default value: 65,536 (bytes)

	      Change the default value of this attribute only if a third-party device driver does not use the ioctl call and has  a  maximum  size
	      that  is less than the default value  (64 KB) in the sysconfigtab file.  (The person writing the third-party device driver must pro-
	      vide information, either in documentation or an installation script, on how to change the entry in the sysconfigtab file to the cor-
	      rect value.)  Default value: 0

	      Do not modify the default setting of this attribute unless instructed to do so by support personnel or by patch kit documentation.

	      Maximum  number  of  NPort I/Os. This attribute is visible only if the Emulex Fibre Channel Host Adapter is installed on the system.
	      Refer to the emx(7) reference page for information on setting this attribute.

	      Default value: 256.

	      To turn I/O limiting off, set the value of NPort_Max_IOs to equal 0xFFFFFFFF.

	      Do not attempt to set the value of NPort_Max_IOs to less than the value of NPort_Min_IOs.

	      Minumum number of NPort I/Os. This attribute is visible only if the Emulex Fibre Channel Host Adapter is installed  on  the  system.
	      Refer to the emx(7) reference page for information on setting this attribute.

	      Default value: 20.

	      The value of NPort_Min_IOs must always be less than the value of NPort_Max_IOs.

	      The  NPort  I/O  ramp time delay in seconds. This attribute is visible only if the Emulex Fibre Channel Host Adapter is installed on
	      the system. Refer to the emx(7) reference page for information on setting this attribute.

	      Default value: 1.

	      The NPort I/O ramp percentage (integer). This attribute is visible only if the Emulex Fibre Channel Host Adapter is installed on the
	      system. Refer to the emx(7) reference page for information on setting this attribute.

	      Default value: 10

	      A query-only attribute used for subsystem debugging.

	      A query-only attribute used for subsystem debugging.

	      An attribute used only internally.

	      Do not modify the default setting of this attribute unless instructed to do so by support personnel or by patch kit documentation.

SEE ALSO

       sys_attrs(5)

																   sys_attrs_io(5)