MongoDB Documentation, Release 3.0.4 11.2.7 Does MongoDB run on Amazon EBS? 11.2.8 Why are MongoDB’s data files so large? 11.2.9 How do I optimize storage use for small documents? See also: $^{7}$https://docs.mongodb.org/ecosystem/platforms/amazon-ec2 Chapter 11. Frequently Asked Questions 748 Shortening field names reduces expressiveness and does not provide considerable benefit for larger documents and where document overhead is not of significant concern. Shorter field names do not reduce the size of indexes, because indexes have a predefined structure. { lname : "Smith", score : 3.9 } In general it is not necessary to use short field names. If you shorten the field named last_name to lname and the field named best_score to score , as follows, you could save 9 bytes per document. { last_name : "Smith", best_score: 3.9 } MongoDB stores all field names in every document. For most documents, this represents a small fraction of the space used by a document; however, for small documents the field names may represent a proportionally large amount of space. Consider a collection of documents that resemble the following: You can store any value in the _id field, but because this value serves as a primary key for documents in the collection, it must uniquely identify them. If the field’s value is not unique, then it cannot serve as a primary key as there would be collisions in the collection. To optimize storage use, users can specify a value for the _id field explicitly when inserting documents into the collection. This strategy allows applications to store a value in the _id field that would have occupied space in another portion of the document. MongoDB clients automatically add an _id field to each document and generate a unique 12-byte ObjectId for the _id field. Furthermore, MongoDB always indexes the _id field. For smaller documents this may account for a significant amount of space. Consider the following suggestions and strategies for optimizing storage utilization for these collections: Each MongoDB document contains a certain amount of overhead. This overhead is normally insignificant but becomes significant if all documents are just a few bytes, as might be the case if the documents in your collection only have one or two fields. Why are the files in my data directory larger than the data in my database? (page 774) • Use the _id field explicitly. • Use shorter field names. See also: Yes. MongoDB users of all sizes have had a great deal of success using MongoDB on the EC2 platform using EBS disks. Amazon EC2 7 MongoDB aggressively preallocates data files to reserve space and avoid file system fragmentation. You can use the storage.smallFiles setting to modify the file preallocation strategy.