I'm in the market for an entry level NAS, and it's between a second hand DS213j and a first hand DS215j. The main difference I'm seeing in the datasheet (https://www.inet.se/files/pdf/4304776_0.pdf) is the move from a single core 1.2GHz (DS213
Last year’s Synology units received a new dual-core processor and we’re pleased to see that even the budget oriented model in this DS215j has also been given the benefit of this too. The DS215j replaces the DS213j and thus adds in more storage