[Observium] Observium Backups

When backing up rrd with tar zcvf observium-rrd.tar.gz rrd I get the following message:

tar: Removing leading `/' from member names

Is this OK or should I use the --absolute-names option?

Also I am getting some messages saying file changed as we read it. This is understandable but do i need to do anything while running the backup to stop this from happening?

Thanks in advance.