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Re: IMP/EXP accross platforms: What will be missing?

From: Howard J. Rogers <hjr_at_dizwell.com>
Date: Thu, 6 Nov 2003 10:48:45 +1100
Message-ID: <3fa98c61$0$9282$afc38c87@news.optusnet.com.au>

"Rick Denoire" <100.17706_at_germanynet.de> wrote in message news:bguiqvskfrlkoped89cumg4d8pd1ac7riv_at_4ax.com...
> "Howard J. Rogers" <hjr_at_dizwell.com> wrote:
>
> >> If importing serially, extents will be allocated so that they will be
> >> physikally contiguous on the harddisk.
> >
> >You can't say that. Extents end up wherever the file system you use deems
it
> >appropriate to put them. Even the blocks of an extent can't be guaranteed
to
> >be contiguous one with another.
>
> OK. But I would expect that the probability of blocks an extents being
> written contiguous is higher when only those blocks and extents are
> being written.

I know it's not strictly comparable, but have you ever looked at the disk defragmenter utility in Windows 2000 (or XP) straight after a fresh install? The thing fragments like crazy. Why? Because (as I understand it), whichever bit of the disk happens to waft under the heads when something needs to be written gets the write. The Windows installer doesn't hang around, incurring rotational latency problems, to make sure the install goes on to disk nice and de-fragmented. Same issue with Oracle, generally speaking. It's better that an extent be written, wheresoever and howsoever, than that we wait for disk rotations to achieve a nice, non-dispersed, arrangement of blocks.

To be fair, it very much depends on your file system. NTFS is not the world's most sensible file system, I realise. So YMMV.

Regards
HJR Received on Wed Nov 05 2003 - 17:48:45 CST

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