Full schedule: Presented by: Dan van der Ster CERN operates several PB-scale CephFS clusters to offer shared storage for IT apps and services. Our lab also developed EOS to deliver high-density, low-cost physics storage and support the APIs needed by the LHC community. This work evaluates CephFS+EOS: CephFS is a reliable low-cost EC backend and EOS is layered on top to add the missing functionalities. We present performance tradeoffs, networking overheads at scale, and optimized Ceph tunings, then conclude with ideas for the future.