Write Anywhere File Layout
| Developer(s) | NetApp |
|---|---|
| Full name | Write Anywhere File Layout |
| Limits | |
| Max. volume size | up to 100 TB (limited by containing aggregate size; variable maximum depending on platform; limited to 16TB when using Deduplication{ONTAP 8.2 now supports dedup to max volume size supported on platform}) |
| Max. file size | up to 16 TB |
| Features | |
| Dates recorded | atime, ctime, mtime |
| File system permissions | UNIX permissions and ACLs |
| Transparent compression | Yes (Ontap 8.0 onwards) |
| Transparent encryption | Yes (since Ontap 9.1; possible with 3rd party appliances like Decru DataFort for older versions) |
| Data deduplication | Yes (FAS Dedup: periodic online scans, block based;) |
| Copy-on-write | Yes |
| Other | |
| Supported operating systems | Data ONTAP |
The Write Anywhere File Layout (WAFL) is a file layout that supports large, high-performance RAID arrays, quick restarts without lengthy consistency checks in the event of a crash or power failure, and growing the filesystems size quickly. It was designed by NetApp for use in its storage appliances.
Its author claims that WAFL is not a file system, although it includes one. WAFL provides mechanisms that enable a variety of file systems and technologies that want to access disk blocks.
One of WAFL's most salient features is the snapshot, or read-only copy of the file system. Zero-copy snapshots allow users to recover files that have been accidentally deleted; they provide an online backup that can be accessed quickly. It is implemented similarly to that of a log-structured file system. A special kind of snapshot that the filer uses internally called a consistency point allows WAFL to restart quickly in the event of an improper shutdown. NetApp's Data ONTAP Release 7G operating system supports a read-write snapshot called FlexClone.
An important feature of WAFL is its support for both a Unix-style file and directory model for clients and a Microsoft Windows-style file and directory model for SMB clients. WAFL also supports both security models, including a mode where different files on the same volume can have different security attributes attached to them. Unix can use eitheraccess control lists (ACL) or a simple bitmask, whereas the more recent Windows model is based on access control lists. These two features make it possible to write a file to a SMB type of networked filesystem and access it later via NFS from a Unix workstation.
As the name suggests Write Anywhere File Layout does not store data or metadata in pre-determined locations on disk, instead it automatically places data using temporal locality to write metadata alongside user data in a way designed to minimize the number of disk operations required to commit data to stable disk storage using single and dual parity based RAID.
...
Wikipedia