  The ROOT TTree data format encodes hundreds of petabytes of High Energy and
Nuclear Physics events. Its columnar layout drives rapid analyses, as only
those parts ("branches") that are really used in a given analysis need to be
read from storage. Its unique feature is the seamless C++ integration, which
allows users to directly store their event classes without explicitly defining
data schemas. In this contribution, we present the status and plans of the
future ROOT 7 event I/O. Along with the ROOT 7 interface modernization, we aim
for robust, where possible compile-time safe C++ interfaces to read and write
event data. On the performance side, we show first benchmarks using ROOT's new
experimental I/O subsystem that combines the best of TTrees with recent
advances in columnar data formats. A core ingredient is a strong separation of
the high-level logical data layout (C++ classes) from the low-level physical
data layout (storage backed nested vectors of simple types). We show how the
new, optimized physical data layout speeds up serialization and deserialization
and facilitates parallel, vectorized and bulk operations. This lets ROOT I/O
run optimally on the upcoming ultra-fast NVRAM storage devices, as well as
file-less storage systems such as object stores.
