Let’s assume your FS is full, for example /opt/oracle (it happens…), and you have no space left on the device. Here’s a simple way to make space:
#tar -cf - * | gzip -c -f - > /var/tmp/optoracle.tar.gz
Just pipe the output of tar to gzip. This way tar won’t create optoracle.tar (which it can’t anyways since the FS is full), but instead write it to gzip which in turn creates the -tar.gz file in /var/tmp.