Re: Raw Devices: Increased Performance?

Paul,

FYI... A potential OPS customer (on Unix) has apparently seen this message and is having second thoughts about buying Oracle Parallel Server because of its requirement of raw disks. We are in the position of having to quiet their fears to finish the sale.

In the case of Oracle on Digital Unix, using raw disk is not as bad as you would make it out to be if the customer uses Digital LSM product, which provides extensive management capabilities.

Although you've included a disclaimer, the outside world will see the "oracle.com" in your email address and take your word as gospel. Please be more sensitive in how you present your opinions.

Thanks.

Jef Kennedy
415/506-6144

In article <4rpsh3$s99_at_inet-nntp-gw-1.us.oracle.com>, pzola_at_us.oracle.com (Paul Zola ) wrote:

> } >joelga_at_rossinc.com (Joel Garry) writes:
> } >
> } >>There was a thread on this a while ago, with some folks claiming minimal
> } >>increase, while others claimed up to 300%.
>
> Let me paraphrase from Cary Millsap's paper "The OFA Standard Oracle7
> for Open Systems", (part number A19308) which everyone in this thread
> should read before posting anything on this subject.
>
> (1) If disk I/O is not the bottleneck, then going to raw devices will
> have *no* *performance* *impact* *at* *all*.
> (2) If disk I/O is the bottleneck, then going to raw devices may
> sometimes gain up to a 10% performance improvement relative to
> the same database using filesystem files.
> (3) Under very common circumstances, going to raw devices can actually
> *decrease* database performance.
> (4) Anyone contemplating going to raw devices should benchmark their
> application on both raw and filesystem devices to see if there is
> a significant performance increase in using raw devices.
> (5) Anyone who does not have the time, expertise, or resources to
> perform the raw-vs-filesystem benchmark *should* *not* *consider*
> using raw devices.
>
> Finally: a word about those 300% speedups that people report. Often,
> when you look at the changes that they've made to go to raw devices
> you'll find that they have done one of:
> (1) Export/Import the database, and thereby remove fragmentation;
> (2) Move control or redo log files onto separate devices or
> controllers;
> (3) Move database files onto separate devices or controllers.
>
> If you adjust for all of the performance improvements that they've
> gotten from all the other optimizations, then you'll see that *just*
> going raw hasn't really bought them that much. Defragmenting, in
> particular, can buy you a *lot* of speed.
>
> Of course, they could always have made the same performance
> improvements without going raw, and gotten most, if not all, of the
> performance gains that they're attributing to raw devices.
>
> -p
>
> ==============================================================================
> Paul Zola Technical Specialist World-Wide Technical Support
> ------------------------------------------------------------------------------
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> reflect the opinions of Oracle Corporation.
Received on Fri Jul 19 1996 - 00:00:00 CEST