Write Anywhere File Layout
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The Write Anywhere File Layout, or WAFL, is a file system designed by Network Appliance for use in their Network File System server appliances. It is designed to support large, high performance RAID arrays and to support quick restarts without lengthy consistency checks in the event of a crash.
One of WAFL's most salient features is the snapshot, or read-only copy of the file system. Snapshots allow users to recover files that they have accidentally deleted; they provide an online backup that can be accessed quickly. Moreover, snapshots allow WAFL to restart quickly in the event of a crash.