MarsSeed [1] filed a deletion request for cassandra21 [2]: Unneeded, broken legacy Cassandra v2.1 (not v21) package from 2018.
AUR has a package for the currently supported release. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/cassandra21/
