Editing Write Anywhere File Layout (section)

===Snapshots===
[[File:Copy On Write technique.png|thumb|Traditional Copy On Write technique data in place backup]]
[[File:NetApp RoW Snapshot (TM).png|thumb|NetApp RoW Snapshot data in place backup]]
WAFL supports ''[[snapshot (computer storage)|snapshot]]s'', which are read-only copies of a file system.  Snapshots are created by performing the same operations that are performed in a consistency point, but, instead of updating the root inode corresponding to the current state of the file system, saving a copy of the root inode. As all data and metadata in a file system can be found from the root inode, all data and metadata in a file system, as of the time when the snapshot is created, can be found from the snapshot's copy of the root inode. No other data needs to be copied to create a snapshot.<ref name="wafl-fs-design"/>

Blocks are allocated when written using a block map, which keeps track of which blocks are in use and which blocks are free. An entry in the block map contains a bit indicating whether the block is in use in the current version of the file system and several bits, one per snapshot, indicating whether the block is in use in the snapshot. This ensures that data in a snapshot is not overwritten until the snapshot is deleted. Using block map all new writes and rewrites are written to new empty blocks, WAFL only reports that block rewrite successful, but no rewrites actually occur, this approach called Redirect-on-write (ROW) technique.<ref name="wafl-fs-design"/> ROW is much faster on rewrite operations compare to [[Copy-on-write]] where old data block going to be rewritten in-place and captured in a snapshot needs to be copied first to space allocated for snapshot reserve in order to preserve original data, this generates additional data copy operations once system get rewrites to that block.

Snapshots provide online backups that can be accessed quickly, through special hidden directories in the file system, allowing users to recover files that have been accidentally deleted or modified.<ref name="wafl-fs-design"/>

NetApp's Data ONTAP Release 7G operating system supports a read-write snapshot called ''[[ONTAP#FlexClone|FlexClone]]''. Snapshots are basis for technologies like [[ONTAP#SnapMirror|SnapMirror]], [[ONTAP#SnapMirror|SnapVault]] and [[ONTAP#Non Disruptive Operations|Online Volume Move]] while features like [[ONTAP#FlexClone|FlexClone]], [[ONTAP#FlexClone|SnapLock]], [[ONTAP#FlexClone|SnapRestore]] are snapshot-like technologies leverage on WAFL capabilities and properties like manipulations with inodes. Starting with ONTAP 9.4 maximum number of snapshots supported for each FlexVol is 1024, while for previous versions max limit was 255.

Starting with ONTAP 9.5 snapshot sharing functionality were added to run deduplication scan across Active file system and snapshots, and deduplication savings is a magnitude of number of snapshots. Before 9.5 not deduplicated data locked in a snapshot couldn’t be used by deduplication process and runs only in active file system.