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support "Asynchronous I/O" or not ?

 
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Eric Unix
Frequent Advisor

support "Asynchronous I/O" or not ?

Hello All

My unix box is -----> HP-UX testserver B.11.23 U ia64 nlimited-user license , and how to know ---> does it support "Asynchronous I/O" or not ?

Thanks a lot.

Eric
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6 REPLIES
James R. Ferguson
Acclaimed Contributor
Solution

Re: support "Asynchronous I/O" or not ?

Hi Eric:

# kctune -v fs_async

See:

http://docs.hp.com/en/B3921-60631/fs_async.5.html

Regards!

...JRF...
Eric Unix
Frequent Advisor

Re: support "Asynchronous I/O" or not ?

Hello James R

Appreciative your great help. Got it now.
If my unix box has high value %wio in sar results, can enable Asynchronous I/O fix this issue ?

Thanks a lot.

Eric
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Eric Unix
Frequent Advisor

Re: support "Asynchronous I/O" or not ?

Hello All

Appreciative your great help. Got it now.
If my unix box has high value %wio in sar results, can enable Asynchronous I/O fix this issue ?

Thanks a lot.

Eric
Look forward
Sani
Frequent Advisor

Re: support "Asynchronous I/O" or not ?



Is it a database server.?
Are you using oracle ?

Eric Unix
Frequent Advisor

Re: support "Asynchronous I/O" or not ?

Hello Sani

Yes, there are oracle db on it and the db is a wharehouse db. Thanks for your kind suggestion. Have a good day.

Best Regards
Eric
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Re: support "Asynchronous I/O" or not ?

Eric,

Although setting the fs_async parameter will allow asynchronous IO ona filesystem, on HP-UX Oracle will ignore this parameter and still open datafiles with the O_DSYNC flag, ensuring it continues to do synchronous IO. On HP-UX the only way to do Oracle asynchronous IO on a filesystem is to use the Veritas QuickIO/ODM modules that come as part of either HP,s Serviceguard Storage Management Suite for Oracle or Symantec's Storage Foundation for Oracle.

Otherwise doing asynchonous IO means not using filesystems, but going for raw, which today means Oracle ASM.

However it's far too simplistic to say that enabling async IO will reduce %wio as there are many other items to take into account (e.g. using multiple DBWR and configuring tabl;espaces across multiple datafiles can get you most of the benefits that async IO would get you), and many other ways of resolving high %wio. You need to carry out a proper perf review to establich what your issue is before proposing a fix.

HTH

Duncan

HTH

Duncan