Re: File System Performance

[Alan Cox]

>         Corrections to speed-up the sizeing pass in Amanda:
>         * tar.h: Declare dev_null_output.
>         * buffer.c (open_archive): Detect when archive is /dev/null.
>         (flush_write): Avoid writing to /dev/null.
>         * create.c (dump_file): Do not open file if archive is being
>         written to /dev/null, nor read file nor restore times.
>         Reported by Greg Maples and Tor Lillqvist.
> 
> One wonders why.

So when you archive the file set twice (once to compute its size) its
faster. Seems sane enough.