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 storage appliances. It is designed to support large, high performance RAID arrays, to support quick restarts without lengthy consistency checks in the event of a crash or power failure, and to support growing the filesystem size quickly.

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, a special kind of snapshot that the filer uses internally called a consistency point allows WAFL to restart quickly in the event of a improper shutdown.

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 for both a Unix-style file and directory model for NFS clients and a Microsoft Windows-style file and directory model for CIFS clients. So, it is possible to write a file to a CIFS type of networked filesystem and access it later via NFS from a Unix workstation. In order to use files with Unix and Microsoft Windows, WAFL has to support both security models. Unix can use either^[1] Access control lists (ACL) or a simple bitmask whereas the more recently Microsoft Windows model for security is based on Access control lists. WAFL provides support for both security models and one mode for using both on the same file.