satellite6: satellite backup / katello-backup is very slow backing up pulp data

Issue

• satellite backup / katello-backup is very slow backing up pulp data
• Running Satellite 6.1.3 on RHEL 7.1 (VMware guest, 12 vCores, 24GB RAM, XFS for /var/lib/pulp) and trying to use katello-backup to backup this install. We have quite a lot of products synced, so that /var/lib/pulp is about 300GB big. As our storage is quite fast (250MB/s), we would expect the backup to take something between 30 and 60 minutes (as pulp data are a lot small files and links, it'd ne probably more on the 60 minute side).

However, the initial run of katello-backup took about 5.5 hours. While inspecting the katello-backup code we noticed that it would try to compress the contents of /var/lib/pulp. These being RPMs and already compressed, this sounds wrong.