Direct I/O on Linux

Some time ago, I inquired on this list about direct I/O on Linux file systems. The idea was to specify direct I/O in init.ora parameter "filesystemio_options". To be able to do that, file system has to support direct I/O, in much the same way like Veritas quick I/O feature. The first candidate I investigated was SGI XFS, but my numerous attempts to get a definitive answer whether XFS supports it or not, the matter is still unresolved.
It is my pleasure to report that the other candidate was much more open and provided a swift answer: JFS does support direct I/O. Here is the answer from Mr. Steve Best, principal IBM's developer of JFS for Linux.

Mladen Gogala wrote:
> Hi Steve!
> I apologize for contacting you directly, but I've been unable to
> get an answer to my question any other way. The question is:
> Does JFS on Linux support direct I/O, i.e. I/O that bypasses buffer
> cache and behaves as if the file was a raw device. In other words,
does
> JFS on Linux has anything like Veritas Quick I/O?.

Yes, the Linux kernel level has to be 2.4.15 or greater. On the 2.5.x kernel level direct I/O is there for JFS also.

> Thanks in advance and I apologize once again for contacting you like
> this.
> --
> Mladen Gogala
> Oracle DBA

Thanks,
Steve

I will test the relative performance of JFS and ext3 file systems this weekend, on my own machine. My prediction is that JFS with direct I/O turned on will be much better then ext3 for updates and index scans, while ext3 will be faster for full table scans (prefetch). The plan is to download the latest version of the driver and link it into 2.4.22 kernel, then generate a table with approximately 1,000,000 records and test full table scans, index scans, serial updates, index updates, deletes and inserts.

-- 
Mladen Gogala
Oracle DBA




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-- 
Author: Mladen Gogala
  INET: mladen_at_wangtrading.com

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