IBM Support

Comparison of the QDLS and "Root" File Systems for Storing User Documents and Other PC Files



This document is intended to assist system administrators determine which file system, QDLS or the "root" file system, is the most suitable to use for storing user documents and other PC files.

Resolving The Problem

To compare file systems, we must first define the Integrated File System.

The Integrated File System is a part of the operating system.  It supports stream input/output and storage management similar to personal computer and UNIX operating systems.  It also provides an integrating structure over all information stored in the server.

The Integrated File System is composed of 11 file systems.  Each file system has its own set of logical structures and rules for interacting with information in storage. This document discusses the QDLS (Document Library - existing in the QDOC library***) file system and the "root" file system.  The document is meant to help system administrators decide which file system is the best repository for user documents, spreadsheets, and other PC files.

Although both file systems can be used to store PC files, there are several differences that must be considered when you decide which to use. The charts at the following URLS display the differences. Review the "root (/)" and QDLS columns.

In almost every case, the "root" file system is the best place to create a repository for user documents, spreadsheets, and other PC files. The most common reasons to use the "root" file system, rather than QDLS, are as follows:
  • No directory entry is required to use the "root" file system.
  • QDLS restricts file names to 8.3 characters with no mixed case, limited special characters, and no spaces in file names, while the "root" file system supports all of these options.
QDLS is an old file system, dating from the System/36 and System/38 days. It is maintained mostly for compatibility with earlier versions. Some applications are hardcoded to store and access files in the QDLS file system. Companies that use those applications are required to use the QDLS file system, upgrade to a newer version of the application, or to migrate to a different application.

Additional information related to both the "root" file system and the QDLS file system is available in IBM Documentation. This information is accessed by going to the IBM Documentation home page at, selecting your version (from the Select drop down menu), and searching for "Integrated File System".

2. Document Library Objects (DLOs) object types include DOC and FLR. They are found within the QDLS file system. Although the objects themselves are stored in library QDOC (in the QSYS.LIB file system), they must never be accessed through the QDOC library. They are not typical IBM i objects and must always be accessed by using the QDLS file system.
3. The allocated file size limit of a document within the QDLS file system is 4 GB - 1. However, only 2 GB - 1 of data can be stored within the document at any time. Therefore, 2 GB - 1 is the effective file size limit of documents within QDLS.

[{"Type":"MASTER","Line of Business":{"code":"LOB57","label":"Power"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SWG60","label":"IBM i"},"Platform":[{"code":"PF012","label":"IBM i"}],"Version":"7.1.0"}]

Historical Number


Document Information

Modified date:
08 June 2021