[CentOS] gtar compression achieved

Wed Feb 1 15:47:03 UTC 2012
Les Mikesell <lesmikesell at gmail.com>

On Wed, Feb 1, 2012 at 8:18 AM, Alan McKay <alan.mckay at gmail.com> wrote:
> Hey folks,
> I looked at the man page and don't see any way to do this - maybe it is a
> function of the compression program used I dunno.
> Is there any way to get gtar to report on the compression it achieved?
> I can't just check file sizes because I'm writing data to tape.
> The basic problem is that I know how much data is there to begin with but I
> don't know how much room it took up on the tape so I have no idea how much
> room is left on the tape.

There is a --totals option, but that is before compression.  I don't
think there is a way to do it.  You can use -f /dev/null and --totals
to get a quick estimate of the uncompressed size of what matches the
tar arguments (for full/incremental).  Gnu tar 'special cases' output
to /dev/null and doesn't bother actually reading the data but it adds
up the sizes from the directory.   That was added so amanda can do
estimates that let it decide how to mix the fulls and incrementals
each day to fill a tape.

   Les Mikesell
     lesmikesell at gmail.com