Emerging fast, persistent memories will enable systems that combine conventional DRAM with large amounts of non-volatile main memory (NVMM) and provide huge increases in storage performance. Fully realizing this potential requires fundamental changes in how system software manages, protects, and provides access to data that resides in NVMM. We address these needs by describing an NVMM-optimized file system called NOVA-Fortis that is both fast and resilient in the face of corruption due to media errors and software bugs. We identify and propose solutions for the unique challenges in adding fault tolerance to an NVMM file system, adapt state-of-the-art reliability techniques to an NVMM file system, and quantify the performance and storage overheads of these techniques. We find that NOVA-Fortis' reliability features consume 14.8% of the storage for redundancy and reduce application-level performance by between 2% and 38% compared to the same file system with the features removed. NOVA-Fortis outperforms DAX-aware file systems without reliability features by 1.5x on average. It outperforms reliable, block-based file systems running on NVMM by 3x on average.