Re: Perfomance problem backupscript (more details and tests)

Les Mikesell <[email protected]> wrote:

> > > ----------------------------------------------------------
> > > wyatt:/# time tar -c  /tmp>/dev/null
> > > real    0m1.054s
> > > user    0m0.212s
> > > sys     0m0.110s
> > 
> > If you like to do a _real_ _test_ why do you compare the star time 
> > against a dummy command?
> > 
>
> In case this isn't clear, gnutar notices when it's output is
> connected to /dev/null and doesn't actually bother reading
> the files in that case.  This is a special case to make
> --times work quickly for estimates like amanada uses to
> decide whether to do a full or incremental run.

And it should be noted that this is badly documented (no man page)
and that the workaround is not mentioned at all:

use GNU tar -c > /dev/zero

It is really bad practice to introduce such an implicit and hidden
feature into a program. Star does it the clean, obvious and easy
to controllable way: use star -onull if you only like to do 
specfic tests for size metering.

Note that GNU tar is even buggy in it's "amanda feature" and badly
fails if you use this "feature" together with sparse files.

Jörg

-- 
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