Concurrent IO on AIX
Juergen Buck asked whether AIX concurrent IO (CIO) matches raw device speed for IDS and has downsides. Barry Leb said CIO needs no Informix-specific setting, he preferred raw, and CIO was about 15 percent faster for DB2. Juergen worried KAIO is lost. Jonathan Leffler noted CIO is a JFS2 option for cooked files and saw no reason not to use it, but had not validated it.
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I heard concurrent IO (cio) is as fast than using raw devices for DB2. Is this also true for IDS ? Is there any negative impact by using CIO instead of raw devices ? Thanks, Juergen
To utilize CIO on DB2 requires a change at the tablespace level. You use an alter tablespace command. I'm not aware of any such similar functionality in Informix. Personally I find it much easier using raw devices with Informix than with DB2. I would stick to raw. I'll also add that CIO does live up to its billing concerning performance. It was considerably faster in the tests we performed, approximately 15% faster. >From: "J'rgen Buck" <juergenb@buck-consulting.de> >To: informix-list@iiug.org >Subject: Concurrent IO on AIX >Date: 16 Feb 2006 07:23:35 -0800 > >I heard concurrent IO (cio) is as fast than using raw devices for DB2. >Is this also true for IDS ? > >Is there any negative impact by using CIO instead of raw devices ? > >Thanks, >Juergen > >_______________________________________________ >Informix-list mailing list >Informix-list@iiug.org >http://www.iiug.org/mailman/listinfo/informix-list
I also think there is no special feature in IDS to use CIO, but if I mount a filesysten with the -cio option and place my chunks there, it should be the virtually the same. My concern is that it's not recommended in the performance guide (at least to my knowledge). I assume it's because I can't use KAIO then. But I'm not sure if it's sigificant slower.
Jürgen Buck wrote: > I heard concurrent IO (cio) is as fast than using raw devices for DB2. > Is this also true for IDS ? > > Is there any negative impact by using CIO instead of raw devices ? There's a document at http://www-03.ibm.com/servers/aix/whitepapers/db_perf_aix.pdf about the performance of CIO. Concurrent IO is an option to JFS2 - journalled file system. Inherently, therefore, it is for use with 'cooked files' rather than raw. Normally, you would not use a journalled file system for a database - the journalling system provides roughly the same functionality that a DBMS provides in terms of atomic changes with recoverability, so you are overlapping the functionality. That said, there's no reason you can't use a JFS for database storage. If your dbspaces are in cooked files on a JFS2 file system, I don't see any particular reason not to use CIO. I've not validated that with anyone - and I've not read every word of the paper, either.
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