The only commerical-backed storage system is the long term storage tape system. Still it has an home-made overlay API over it to interface with the rest of the systems.
All their important "administrative" stuff (think Active Directory/LDAP user database, mail and other essential services) run on proprietary storage systems from a commercial vendor (not IBM though), with enterprise support and all.
At least that was the case a few years ago when we last talked to one of the heads of IT at CERN, but I guess it hasn't drastically changed
Most internal data is spread between Ceph and home-made distributed storage system named EOS (https://indico.cern.ch/event/138478/contributions/149912/att...) running over commodity hardware.
The only commerical-backed storage system is the long term storage tape system. Still it has an home-made overlay API over it to interface with the rest of the systems.