Do not mirror delta rpms by default

[dirkmueller]

Checking the SUSE CDN logs, we see that RMT / SMT servers are downloading delta rpms. zypper(1) is falling back gracefully if drpms are not available, and downloading them to store locally seems like a waste of bandwith and storage, as the RMT setup is close / high bandwidth to the actual machines that want updates, and delta rpms make no sense there.

So much they don't make sense that there is a discussion to turn it off client side even:

openSUSE/libzypp#620

[digitaltom]

Disabling the download on delta RPMs is likely changed here: https://github.com/SUSE/rmt/blob/master/lib/rmt/mirror/repomd.rb#L64
We would need to investigate if there can be issues on the client side, when those delta RPMs are not available on RMT, because the repo metadata still references them, we cannot rewrite the metadata.

[dirkmueller]

libzypp clients will silently ignore failures on delta rpms and fall back to the full rpm. dunno about other clients though.

[rjschwei]

Having the option to disable drpm mirroring would be great.

[digitaltom]

Dev task: https://trello.com/c/ynAMY9RW/3818-do-not-mirror-drpms-by-default-on-rmt