writing large files quickly

Donn Cave donn at u.washington.edu
Fri Jan 27 15:30:49 EST 2006

In article <drduvt$m6r$1 at solaris.cc.vt.edu>,
 rbt <rbt at athop1.ath.vt.edu> wrote:
> Won't work!? It's absolutely fabulous! I just need something big, quick 
> and zeros work great.
> How the heck does that make a 400 MB file that fast? It literally takes 
> a second or two while every other solution takes at least 2 - 5 minutes. 
> Awesome... thanks for the tip!!!

Because it isn't really writing the zeros.   You can make these
files all day long and not run out of disk space, because this
kind of file doesn't take very many blocks.   The blocks that
were never written are virtual blocks, inasmuch as read() at
that location will cause the filesystem to return a block of NULs.

   Donn Cave, donn at u.washington.edu

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