Re: Raw device 8.1.7.4.0 Linux

Mladen Gogala wrote:

> On Sun, 07 Dec 2003 18:36:50 -0800, Daniel Morgan wrote:
>

>>What nightmare with raw devices? In my experience, mostly with AIX, they 
>>are a few mouse clicks and never a thought except that little 
>>calculation of how much free space to leave behind.

Of course. The point with a raw device is that you define the size you want and grab as close to 100% of it as possible. There is zero value in leaving any space unused as, not being a file system, there isn't anything else you can use it for.

  it is
> very hard to back them up, you cannot use tar or cpio and copying them to
> another disk is a real pain. Using raw devices mandates purchase of
> expensive 3rd party backup software (good luck with dd).

I'll agree that some 3rd party backup is essential, or nearly so. But that is a question of dollars and budges. Not to use your word a "nightmare" for the technology people.

  Last but
> not least, creating raw devices is a privileged operations that involves
> SAs and, usually, cannot be done by a DBA.

So is anything else on a properly managed UNIX box.

  The only situation when raw
> devices are what you really, really want is when you have a RAC (in case
> of 8i, it's OPS). Should I say that all of the operations listed above are
> quite easy with an ordinary file system?

Ease is not the issue. The issue is performance.

  You are on AIX, which comes
> with a native implementation of JFS. JFS supports both direct IO and async
> IO, which means that you can use ordinary files with the same efficiency
> as raw devices. Have you ever benchmarked JFS vs. raw on AIX? I haven't,
> but I'll buy you a pizza and a drink if the difference is significant.

The SA said the difference was measurable. I do Oracle he does 5L.

-- 
Daniel Morgan
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http://www.outreach.washington.edu/ext/certificates/aoa/aoa_crs.asp
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