sys_attrs_io(5)sys_attrs_io(5)NAMEsys_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 accom‐
modate 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.
An integer value of 0 or 1. A value of 1 (the default) forces
the boot to wait for all device registrations before the login
prompt. A value of 0 results in a boot to the login prompt with‐
out waiting for all device registrations to be completed.
Setting the value to 0 provides the greatest speedup in booting.
This setting makes the entire storage subsystem accessible
before all registrations are completed, although it does result
in an incomplete hierarchy view from the commonly used hwmgr
utility until all registrations are complete.
The hwc_registration_complete attribute can be queried to check
on the status of device registrations. This will be set to 1
when all registrations are complete.
The hwc_reg_cmplt_notify_type attribute controls the notifica‐
tion when device registration is complete. This can be set to
generate a console message, an EVM event, or both. (See
hwc_registration_complete and hwc_reg_cmplt_notify_type)
There are three ways to determine when hwmgr can be run to see
the complete hierarchy: If the EVM notification option is
enabled, you can log in and start evmwatch to look for the EVM
event, although the EVM event could have already occurred
before the log in. If the console log message notification
option is enabled, you can look in the messages file for the
message. The sysconfig I/O subsystem hwc_registration_complete
attribute can be queried. This will be set to 1 when registra‐
tions are complete. This option can be used regardless of how
the notification options are set.
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 allo‐
cated from the kernel. More buffers are allocated from the ker‐
nel 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 mem‐
ory (rather than starting with a lower number and letting the
system dynamically increase it when necessary) may improve per‐
formance. 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 num‐
ber of ccbs. Any performance improvement that results from a
cam_ccb_pool_size increase can occur only if your system's mem‐
ory 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 cde‐
vsw_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 docu‐
mentation.
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 sup‐
port 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 sup‐
port 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 sup‐
port personnel or by patch kit documentation. An integer that
controls notification when device registration is done. Possible
values are:
0 (The default, no notification)
1 (Print message on console)
2 (EVM event only)
3 (Both console message and EVM event)
The console message reads “All paths have been registered.”.
The EVM event is sys.unix.hw.all_paths_registered.plat‐
form.*.*.*.* An integer value that can be queried to determine
if device registration is complete. The value will be 0 when
device registration is not yet complete and 1 after it is com‐
plete. This value is always available, regardless of how
hwc_reg_cmplt_notify_type is set.
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 kilo‐
bytes) 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.)
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 docu‐
mentation.
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; how‐
ever, 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 docu‐
mentation.
SEE ALSOsys_attrs(5)
Tru64 UNIX Hardware Management
sys_attrs_io(5)
