You need to choose the appropriate metaphor to design effective icons. Folders are the appropriate metaphor for a storage container for documents because people use folders to store pieces of paper. In contrast, most people probably wouldn't use a kitchen canister for storing documents.
People do use canisters to store things, and the shape of a hard disk platter is round.
But it would require a major leap of logic for people to associate a canister as a storage medium for something like paper. Figure 8-9 illustrates this point. Inc. All rights reserved.