Re: Raw Devices: Increased Performance?

From: MarkP28665 <markp28665_at_aol.com>
Date: 1996/07/08
Message-ID: <4rsgqe$4tn_at_newsbf02.news.aol.com>#1/1


My employer has had two Oracle dbms experts on site to look over our system. We paid a very high hourly rate (rumored to be 275.00/hour) for these people and we kept them each for a minimum of five days. Both recommended that we run on raw partitions and not UNIX file systems.

Raw partitions usually result in a 50% performance improvement for an individual physical I/O and this generally results in a 10% performance impovement for the database as a whole. Going to raw partitions with NOT help much if the problem is bad code. Most performance improvements will come from rewriting SQL and changing how applications work, not from changing the database.

Raw partitions are not any harder to manage than UNIX file system files if you plan your system out in advance and follow a few simple rules. You can move raw partitions around and redefine where they are located via UNIX without having to rename them via Oracle. Oracle should be stopped at the time, but we have done it several times to move files to new disks.  Switch from 'cpio' and 'tar' to 'dd' or the vendor provided fast character special data set copy utility for your backups and what real difficulity do raw partitions present.

In the old days raw partitions were superior than UNIX files because UNIX controls the buffering of the I/O and buffers recorded as written by Oracle could in fact not be written. With raw partitions the I/O is unbuffered by the OS. Most, but not all, modern UNIX system provide a write through the buffer function which tells UNIX not to buffer the I/O. Oracle development uses the unbuffered call when available or so one of the experts told me after talking to a private internal support resource. If your UNIX system does not support the write-thru the buffer method you may want to switch to protect your data.

Some Oracle options like parallel server (not query) require the use of raw partitions so you may not have an option. And as far as the Millsap paper goes I was advised by a friend with an inside contact in development to read it with a grain of salt because it was written to address the needs of Oracle support who mostly support small installations where the depth of knowledge is shallow, and because application developers always point to the database as the problem and not their code.

UNIX files systems work fine for most shops, but if you need every bit of performance that you can get then you should switch to raw partitions. This could be an endless discussion. Received on Mon Jul 08 1996 - 00:00:00 CEST

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