[Gllug] Reiserfs faster boot

[Simon Trimmer]

On 7 Oct 2001, Darran D. Rimron-Molloy wrote:
> > What exactly is hole creation in filesystem terms?  Excuse my
> > ignorance.
>
> When you create a file that contains the same character repeated (ed,
> cat /dev/zero into a file - say a couple of megs worth of 00000's ) it
> won't take a couple of meg, it takes only a few bytes. That's a hole in
> the file-system.
>
> But cat'ing your newly created file still returns multi-millions of 0's
> - or whatever.
>
> Then again, how often do you create a hole in a file-system?
>
> Or have I got this wrong - atleast that's what I thought a hole in the
> file-system was....

Right, though holes are generally accepted to be zeros as loads of zeros are
much easier to create than blocks of a another value so I wonder if a linux
filesystem is advanced enough to repeating-non-zero-patterns (filesystem
internals discussion skipped).

Holes turn up a lot more frequently than you'd imagine, if you consider a
block is only 512b or 1k you often find holes in binary files. A while back I
saw some problems copying kernel images between a dos and ext filesystem -
the image was getting corrupted because cp+dos filesystem didn't deal with
holes properly (tip: cat is your friend)

-Simon
Simon Trimmer <simon at urbanmyth.org>



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