How does filling a disk to capacity affect performance?

[fsinf at iravcl.ira.uka.de]

In article <460 at osupyr.mast.ohio-state.edu>, czei at osupyr.mast.ohio-state.edu (Michael S Czeiszperger) writes:
> [...] the 'df' command adjusts the reading so that when it says 100% full,
> the disk really is only 90% full.  It goes on to say that having the
> disk over 90% would affect its performance.  Does anyone know [...]
> if there are any reasons not to keep a disk at 96-99%??????

Maybe the reasons are ...
I've heard (but not verified) you can crash *every* unix-system using the
CP-command when there is not enough space on disk. CP will not check
whether the disk is full and overwrite blocks which are not free. The original
data will be lost; also the machine is likely to go down.

If this isn't right, please correct.

Regards, Elmar
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