Tim Kientzle <t...@kientzle.com> wrote:
> I'm curious. If someone types the following command:
>
> tar cf /dev/null some files
>
> What do you think they expect to happen?
Of course that all files are read. POSIX does not allow different behavior just
because the output is connected to a different sink.
Maybe this is why n-1 tar implenentations implement a uniform behavior.
Star implements a special documented option for the case that a user is
interested in getting the size of the archive to be created quickly.
If one user (amanda) expects side-effects, I would see this as a bug.
tar cf /dev/null some files
Is used by many people to do one of the following:
- Do speed tests for the underlying filesystem
- Give the OS the opportunity to cache data and meta data
- Make sure that all data and meta data in a filesystem is read
in order to trigger disks to do auto-reallocation on blocks
that are going to become bad.
- Make sure that all data and meta data in a filesystem is readable
Gtar does not allow this to be done easily and keep in mind that many OS
implementations have a significant performance loss when using pipes.
Jörg
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