Does ONTAP apply efficiency to blocks that only exist in Snapshots?
Applies to
- ONTAP 9
- Active Filesystem (AFS)
- Snapshot
- Efficiency
- Deduplication
- Compression
- Compaction
Answer
No, ONTAP does only deduplicate blocks that exist in active filesystem (AFS).
Additional Information
- Once a block got deleted from AFS but still exists in a snapshot, subsequent efficiency operations do not consider that block for deduplication anymore.
- There is parameter
-snapshot-blocks true
undervolume efficiency start
when run withset advanced
privileges. This does not run deduplication but compression only against snapshot-only blocks that do not exist in AFS anymore.
Example:
- File or Block was written to a volume
- Inline efficiency was NOT applied
- FAS with no inline configured
- AFF under high write workload (inline is best effort)
- Written block is tracked in volume efficiency changelog, to be picked up by next efficiency background job
- Background efficiency job schedule did NOT yet trigger
- Snapshot
snap1
is created - File or Block written in 1. is deleted from AFS and so remains trapped in a Snapshot
snap1
only - Background efficiency schedule triggers
- File or Block written in 1 remains in WAFL (
snap1
) without deduplication applied until Snapshotsnap1
is deleted