5 Things to Know About ZFS Dedup and RAM

Dedup requires the entire DDT in RAM ZFS deduplication performance depends on the dedup table (DDT) living entirely in RAM. If it spills to disk, performance drops dramatically.

8GB is already insufficient Even with modest datasets, the DDT can be gigabytes. 8GB of RAM puts you in a bad spot for dedup.

16GB does not fix dedup Upgrading from 8GB to 16GB gives a bit more room, but the DDT will still spill to disk. Dedup only works well with enough RAM to hold the entire table.

For a small home NAS, aim for 64GB or more To reliably hold the DDT for typical datasets, you usually need at least 64GB of RAM.

16GB improves caching, not dedup The extra RAM in 16GB benefits the ARC (Adaptive Replacement Cache), improving general read performance. Do not buy 16GB expecting better dedup.