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The Data Domain file system includes a nonvolatile RAM (NVRAM) write buffer into which it puts all data not yet safely on disk. The file system leverages the security of this write buffer to implement a fast, safe restart capability.
The file system uses many internal logic and data structure integrity checks. If one of these checks finds any problem, the file system restarts itself. The checks and restarts provide early detection and recovery from data corruption errors. As it restarts, the Data Domain file system verifies the integrity of the data in the NVRAM buffer before applying it to the file system, ensuring that no data is lost due to the restart. Because the NVRAM is a separate hardware device, it protects the data from errors that can corrupt data in RAM. Because the RAM is nonvolatile, it also protects against power failures. Though the NVRAM is important for ensuring the success of new backups, the file system guarantees the integrity of old backups even if the NVRAM itself fails.