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The OneFS journal, which stores information about changes to the file system, is designed to enable fast, consistent recoveries after system failures or crashes. The file system replays the journal entries after a node or cluster recovers from an outage.
Each Azure VM node contains local SSD storage, also known as temporary disk. OneFS leverages one of the local SSD as the journal target storage for protecting uncommitted writes to the file system. When a node boots up, it checks its journal and selectively replays transactions to disk where the journaling system deems it necessary.