PRIMS: making NVRAM suitable for extremely reliable storage

Non-volatile byte addressable memories are becoming more common, and are increasingly used for critical data that must not be lost. However, existing NVRAM-based file systems do not include features that guard against file system corruption or NVRAM corruption. Furthermore, most file systems check consistency only after the system has already crashed. We are designing PRIMS to address these problems by providing file storage that can survive multiple errors in NVRAM, whether caused by errant operating system writes or by media corruption. PRIMS uses an erasure-encoded log structure to store persistent metadata, making it possible to periodically verify the correctness of file system operations while achieving throughput rates of an order of magnitude higher than page-protection during small writes. It also checks integrity on every operation and performs on-line scans of the entire NVRAM to ensure that the file system is consistent. If errors are found, PRIMS can correct them using file system logs and extensive error correction information. While PRIMS is designed for reliability, we expect it to have excellent performance, thanks to the ability to do word-aligned reads and writes in NVRAM.