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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.
basic_dma_window_size
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.
bdevsw_size
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/system_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.
booted_media
A query-only attribute that specifies the media from which the system
was booted.
cam_ccb_increment
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.
cam_ccb_low_water
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.
cam_ccb_pool_size
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.
cdevsw_size
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.
device_switch_inited
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.
device_switch_print
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.
device_switch_stale
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.
dma_dac_capable
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.
dma_sg_map_64bit
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.
dma_sg_map_unload_zero
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.
force_envmon
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.
max_iosize_read
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 nondriver
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 sysconfigtab file to the
correct value.)
max_iosize_write
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 nondriver
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 provide information, either
in documentation or an installation script, on how to change the entry
in the sysconfigtab file to the correct value.)
no_scatter_gather
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.
NPort_Max_IOs
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.
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.
NPort_IORamp_Delay
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.
NPort_IORamp_Percent
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
* parallel_edt_scan
A value that determines whether SCSI and Fibre Channel buses are
simultaneously (1) or sequentially (0) probed for devices.
Default value: 0 (sequential probing)
Setting parallel_edt_scan to 1 can significantly reduce the boot time
for systems with moderate to large numbers of devices; however, the
identifiers given any new devices may not be assigned in a contiguous
sequence. See the section on parallel scanning in the Hardware
Management manual for detailed information.
root_dev
A query-only attribute used for subsystem debugging.
root_hardware_id
A query-only attribute used for subsystem debugging.
root_mounted_rw
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)
Tru64 UNIX Hardware Management
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