I love SnapDiff not because it's my favourite ONTAP feature, but because understanding SnapDiff forces you to understand WAFL.

SnapDiff compares the WAFL metadata trees of two snapshots. Shared block pointers allow it to prune unchanged regions. It then examines changed inode and directory metadata to identify created, deleted, modified, and renamed filesystem objects. WAFL is a tree rooted at a root inode.


WAFL filesystem is represented as a tree of blocks:

  • root inode
  • inode file
  • metadata blocks
  • indirect blocks
  • data blocks


Metadata lives in files, WAFL stores metadata in files, including:

  • inode file
  • block map
  • inode map


and that the root inode points to the inode file.


When NFS is enabled on a LIF for API access, but not data access, SnapDiff is limited to these actions:

  1. compares two snapshots,
  2. traverses the filesystem internally,
  3. compares snapshot metadata,
  4. generates change lists for backup applications



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