sys_attrs_io - io subsystem attributes
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/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.
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 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 thirdparty
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.)
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.) 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 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.
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.
sys_attrs(5)
Tru64 UNIX Hardware Management
sys_attrs_io(5)
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