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 Fabric Attached Server series, or FAS series, storage 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 or power failure.

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.

Its implementation is similar to that of a Log-structured filesystem.

Network Appliance's Data ONTAP Release 7G operating system supports a read-write snapshot called FlexClone.

One of the most important features of WAFL is the support of CIFS, Network File System and HTTP, called Multiprotocol Data Access. So, it is possible to write a file to a Windows share and access it later via NFS from an Unix workstation. In order to use files with Unix and Windows, WAFL has to support both security models. Unix uses a simple bitmask whereas the Windows Security model is based on Access control lists. WAFL provides a file mode for each security model and one mode for using both on the same file.