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)