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AIX and Largefiles Performance

From: Byron Pearce <>
Date: Fri, 25 Jun 2004 15:50:42 -0500
Message-ID: <>


I am not a native of Planet IBM, but this morning one of the systems administrators here forwarded over a tuning guide from the mother ship regarding Oracle on AIX. There were a number of interesting things in there that I am still working through, but one particular item piqued my interest.

"... Do not allocate a JFS with the large file enabled (bf) attribute. The big file attribute increases the minimum DIO transfer size (diocapbuf.dio_min returned by the finfo system call) from 4K to 128K, forcing Oracle to read and write a minimum of 128K byte to exploit DIO. Please note that 2GB is the largest file size applications (including Oracle) can use in a JFS without the 'bf' attribute -- large file enablement. Do not allocate a compressed JFS, which defeats DIO. Respecting the JFS 2GB maximum file size avoids potential file level inode locking performance issues in JFS or JFS2 (without CIO), but a downside of small (2GB) files in a very large database (VLDB) environment is the time required to open/close files during the startup/shutdown."

I have worked on most of the other major O/S variants, and this is the first time I have ever heard the largefiles settings have a negative impact on performance. In the interest of scientific investigation on this topic, I am officially checking my ego at the door and opening my mind to this possibility. I am trying to do some research on this, but, thus far, my findings have been sparse.

Has anyone heard this before? Or is this a performance myth along the lines of the BCHR's (if so it is a first for me to hear it)? Or is there a genuine benefit to be gained by doing this?

Any comments or thoughts on this matter would be appreciated.


Byron Pearce               
Tenure Systems, Inc.                 Dallas/Fort Worth, TX

"It's hard to be a ninja when you wear a beeper."

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Received on Fri Jun 25 2004 - 15:48:04 CDT

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