Re: strange df output?
H. Peter Anvin (hpa@transmeta.com)
Mon, 3 Jun 1996 08:31:20 -0700 (PDT)
> >
> > : Part of the function of the reserved space is to make
> > : sure there is enough free space to let the block placement algorithms
> > : work efficiently.
> >
> > Put another way, these numbers are based on how well a hash table
> > performs when the alpha of the table (its load) gets high. Most of
> > these systems use a hash table to know what it can allocate.
>
> I believe the BSD 10% is actually a lot simpller to explain, the
> (original) algorithm trys to do various optimizationes, one is to
> find a contiguous space to put the file in and another is to do so
> all in one track. The chances of finding such a place in the file
> system (for files of more than a few blocks) drops quite fast as the
> disk nears 100% full. So the OS wastes time first to discover that
> there is no suitable place to write the file, and secondly having to
> fragment the file on disk. An easy way to avoid too much
> fragmentation is to simple leave 10% of the disk free.
>
You know, guys, we have just explained the same thing three
times... it's the same thing.
-hpa