Board Thread:Questions and Answers/@comment-65.31.79.34-20140322203046/@comment-86.139.80.113-20140327170728

A Deep Storage Unit (a.k.a DSU) is a type of advanced chest that can hold up to two billion of a single block type; a DSU can be picked up and moved without it dropping its contents on the floor.

N.B. However if a DSU has fewer than 65 of an item in it when it is picked up then it will drop all of its contents on the floor in the same way a regular chest does.