Introduction#

Like most modern operating systems, IBM i relies on multiple filesystems. This post will present the local filesystems currently supported.

Library filesystem (QSYS.LIB)#

This is generally the most well known and used filesystem.

It is a non hierarchical filesystem (objects are in a library but a library cannot be in a library).

The library and the object name can be up to 10 characters long. The object type can be up to 6 characters long. The filesystem is (mostly) case insensitive.

The notation is library/object (that was changed from the S/38 notation object.library).

In the IFS, this filesystem is accessible in /QSYS.LIB.

Documents and folders (DLOs or QDLS)#

This is the original hierarchical stream oriented filesystem before the IFS was introduced in V3R1.

It uses the MS-DOS naming convention (up to 8 character name plus 3 characher extension all case insensitive).

The documents are actually stored in the QDOC library (plus QDOCnnn for user ASPs).

While still officially supported by IBM, this filesystem has many limitations and poor performances compared to the IFS. Its used is discouraged.

In the IFS, this filesystem is accessible in /QDLS

root filesystem (/)#

Often also called the integrated filesystem. It is a hierarchical filesystem very similar to unix filesystems.

One key difference with most unix filesystems is that the root filesystem is case insensitive (you can’t have 2 files named Foo and foo in the same directory) but it will store a file case when created.

As the name implies, this filesystem is the root of the IFS (/).

QOpensys filesystem#

QOpenSys is almost identical to the root filesystem, notably, QOpenSys is case sensitive.

In the IFS, it is accessible in /QOpenSys.

Optical filesystem (QOPT)#

The optical filesystem is a hierarchical filesystem used to access optical media.

In the IFS, it is accessible in /QOPT.

User defined filesystem (UDFS)#

User defined filesystems are similar to the root and QOpenSys filesystems but can be created in a set ASP or independent ASP.

They are mounted in an existing directory in the IFS.

This is all the local filesystems IBM i supports.