File '/dev/async' not present :errno=2

[Ankit Agrawal]

Hi,
My customer wants me to create '/dev/async' file.
what should i do?
well is there any side effect of creating this file or it will degrade performance.
Because this is production server where they want me to do so.
please help me,i am new in HPUX

[AwadheshPandey]

http://hpux-tips.blogspot.com/

[AwadheshPandey]

http://forums12.itrc.hp.com/service/forums/questionanswer.do?admit=109447627+1206511691780+28353475&threadId=974807
http://forums12.itrc.hp.com/service/forums/questionanswer.do?admit=109447627+1206511747829+28353475&threadId=998878
http://www.dbasupport.com/forums/archive/index.php/t-38592.html

[Kapil Jha]

I don think there is anyside effect of creating this file
/sbin/mknod /dev/async c 101 0x0
/usr/bin/chown oracle:dba /dev/async
/usr/bin/chmod 000 /dev/async

It has some impact on IO but would reduce message , which u can safely ignore.
BR,
Kapil

[Ankit Agrawal]

Thanks for your answers.
But the driver "asyncdisk" is also not inserted in kernel so is it required to insert asyncdisk driver in kernel to use async io feature

[Yogeeraj_1]

hi Ankit,

>File '/dev/async' not present :errno=2
You will also observe several trace files are generated with the error message

If the "/dev/async" device does not exists, you need to create it using the root user as mentioned above by kapil:

/sbin/mknod /dev/async c 101 0x0
/usr/bin/chown oracle:dba /dev/async
/usr/bin/chmod 000 /dev/async

The permissions on /dev/async of 000 ensure that it is not possible to use the async driver unintentionally.

Also, you will have to modify the "init.ora" - parameters:

disk_asynch_io = false
tape_asynch_io = false


There should not be any "side-effect" or degradation expected.

To be noted that starting from Oracle10g, async I/O is enabled by default (even if the OS is not configured for it). This is based on the value of the DISK_ASYNCH_IO parameter in the database initialization parameter file. The default value is TRUE.

On the other side, you may wish to to avoid these error messages and trace files, by setting DISK_ASYNCH_IO=false in the init.ora file (or spfile) and restart the instance.


hope this helps!
kind regards
yogeeraj

[D.Blond · Accepted solution]

Hi,
Kernel :

a. configure the async driver in the kernel
Using SAM
-> Kernel Configuration
-> Drivers
-> the driver is called 'asyncdsk'
Generate new kernel
Reboot

b. set max_async_ports
Using SAM
-> Kernel Configuration
-> Configurable Parameters
-> max_async_ports ï   1024

max_async_ports limits the maximum number of processes that can concurrently
use /dev/async. Set this parameter to the sum of
'processes' from init.ora + number of background processes

The background processes started at instance startup will open /dev/async
twice.

If max_async_ports is reached, subsequent processes will use synchronous i/o.


c. set aio_max_ops
Using SAM
-> Kernel Configuration
-> Configurable Parameters
-> aio_max_ops

aio_max_ops limits the maximum number of asynchronous i/o operations that
can be queued at any time. Set this parameter to the default value (2048),
and monitor over time (use glance).

Maj au niveau HP-UX:

ll /dev/async
crw-rw-rw- 1 bin bin 101 0x000000 Dec 19 14:08 /dev/async
rm /dev/async
mknod /dev/async c 101 0x000004
Le 0x040000 gére les time_out
ll /dev/async
crw-r--r-- 1 root sys 101 0x000004 Jan 25 15:59 /dev/async
chmod a+w /dev/async
ll /dev/async
crw-rw-rw- 1 root sys 101 0x000004 Jan 25 15:59 /dev/async
cat /etc/privgroup
cat: Cannot open /etc/privgroup: No such file or directory
echo "dba MLOCK" >> /etc/privgroup
cat /etc/privgroup
dba MLOCK
/usr/sbin/setprivgrp dba MLOCK

[Ankit Agrawal]

well.Thank you so much for your answers.
Can you guys please give me last sugesstion.
Will it be benificial to create /dev/async without inserting asyncdisk driver.