In FreeNAS 8.3 deduplication can be enabled at the dataset level and there is no way to undedup data once it is deduplicated. The more data you write to a deduplicated dataset the more RAM it requires – importing an unclean pool can require between 3-5 GB of RAM per TB of deduped data and if the system doesn’t have the needed RAM it will panic. Think carefully before enabling dedup!
