topic Re: /dev/async in Operating System - HP-UX

/dev/async

Robert Holliday_1 — Tue, 02 Dec 2003 14:03:08 GMT

My Oracle dba has requested that I remove the /dev/async driver. He wants to reduce the number of errors reported to the log file. I have not read his error log to get the full picture yet. I have read the numerious postings on this driver from this site.

If, I remove this driver will performance be improved or degraded?

What will be the benefit of removing the /dev/async driver?

I have a real concern about the benefits of this request.

Re: /dev/async

Helen French — Tue, 02 Dec 2003 14:16:57 GMT

I remember reading, that the async driver caused performance degradation on Sybase database server. But in that case the real solution was to recreate the async driver with another minor number. Check your with:

# ls -al /dev/async

On system performance, async drivers does have the impacts especially on I/O process. I would defenitely consider checking what's the real reason behind your issue, before removing the driver from the system.

Re: /dev/async

Robert Holliday_1 — Tue, 02 Dec 2003 14:22:40 GMT

# lssf /dev/async
pseudo driver asyncdsk minor 0x000000 /dev/async

Also, dba MLOCK does exist in /etc/privgroup

Thanks for your advice

Re: /dev/async

Helen French — Tue, 02 Dec 2003 14:28:51 GMT

I would first check with the dba for the reason behind removing this driver. If convinced, then try recreating it with:

# mknod /dev/async c 101 0x00000?

The last digit can be:
0x000000 default
0x000001 enable immediate reporting
0x000002 flush the CPU cache after reads
0x000004 allow disks to timeout
0x000005 is a combination of 1 and 4
0x000007 is a combination of 1, 2 and 4

(Refer TKB #UPERFKBAN00000726)

Re: /dev/async

Helen French — Tue, 02 Dec 2003 14:31:50 GMT

Again, apply all latest patches too. There are a number of patches (Kernel, subsystem etc) which directly affects the async driver and it's functions. In HP-UX 11i, there is a patch for the driver itself (PHKL_25506). Also, check your Kernel parameters and see if it enables the driver on Kernel.

Re: /dev/async

Robert Holliday_1 — Tue, 02 Dec 2003 16:11:38 GMT

Thank you for your guidance. It turns out the dba had a production problem. He wanted the /dev/asysc file removed because he believed it was the cause of the trace error messages.

I ran the getpriv dba on the test server and the response was:
# getprivgrp dba # Test server
dba: MLOCK

# getprivgrp dba # Prod server
dba:

It turns out that the /etc/privgroup had a typo in it.
cat /etc/privgroup
dba MBLOCK

Bingo! Problem found.

Thanks for your help.

Re: /dev/async

A. Clay Stephenson — Tue, 02 Dec 2003 16:15:19 GMT

The moral of this story:

Get your DBA to describe the problem NOT what he thinks the solution will be.