Re: Linux Oracle 9.2 File mapping

On Wed, 08 Oct 2003 17:51:44 +0200, Peter BUSS wrote:

> Hi,
>
> I can't find the filemap.ora file under $ORACLE_HOME/rdbms/filemap/etc
> as written in the book (oracle dba adm, page 393, step 1). This is
> for working with volume managers. Anyone ?
>
> Peter

Wrong. File mapping parameters are for working with SAN, and only the supported varieties, like EMC. See Metalink, note 177498.1. If you really want to do something for the performance of your oracle 9.2 on Linux, my advice is to put all files on JFS (IBM file system) and set your filesystemio_options to setall. Works like a charm, regardless of whether JFS is used on top of LVM or not. As for file mapping, that library should be supplied by your favorite SAN vendor. Direct I/O, on the other hand, bypasses Linux buffer cache and avoids double buffering, in a similar fashion like Veritas Quick I/O. With direct I/O you get all the advantages of raw devices, without any problems connected with raw devices. Ext3 and ReiserFS do not support direct I/O. Ext2 does, with a patch. Ext2, on the other side, is not a journalling file system, so you can expect to have some fun with fsck when it needs to be done. JFS is a journalling file system, the only production strength file system supporting both async I/O and direct I/O on Linux. It's not the fastest thing in the file system benchmarks, but it certainly does improve performance of the oracle on Linux. I don't have any particular measurements, but the performance improvement comes from avoiding double buffering, thus saving some overhead (insignificant) and avoiding paging and thrashing when the system is under heavy load.

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