Recently I came across a case where deduplication ratio for the same data is lower on NetApps than on ZFS. This document maybe explains why - see limits for dedup on NetApp starting with page 26. Apparently NetApp will silently stop deduping data after a specific limit which varies for different models and Ontap versions is reached.
Anyone has some other ideas why effectiveness of dedup on ZFS might be higher for the same data? (assuming the same or similar blocksize).