  Tvarak efficiently implements system-level redundancy for direct-access (DAX)
NVM storage. Production storage systems complement device-level ECC (which
covers media errors) with system-checksums and cross-device parity. This
system-level redundancy enables detection of and recovery from data corruption
due to device firmware bugs (e.g., reading data from the wrong physical
location). Direct access to NVM penalizes software-only implementations of
system-level redundancy, forcing a choice between lack of data protection or
significant performance penalties. Offloading the update and verification of
system-level redundancy to Tvarak, a hardware controller co-located with the
last-level cache, enables efficient protection of data from such bugs in memory
controller and NVM DIMM firmware. Simulation-based evaluation with seven
data-intensive applications shows Tvarak's performance and energy efficiency.
For example, Tvarak reduces Redis set-only performance by only 3%, compared to
50% reduction for a state-of-the-art software-only approach.
