Reliance Edge

Reliance Edge is a small, portable, highly reliable power-fail safe file system for resource-constrained embedded systems like microcontrollers. It is written in C and provides a familiar POSIX-like file system API, making it easy to use in your application; or an alternate minimalist API if your application has simple storage needs. Reliance Edge is highly configurable and can be tuned to the precise needs of your application.

Getting Help

You will find this section later in our readme as well - but we wanted to tell you up front: DATALIGHT WANTS TO HEAR FROM YOU! Whether it‘s just to make comments about the product, to suggest new features, or to tell us what you don’t like - reach out! All comments and inquiries can be directed to


The complete documentation for Reliance Edge is distributed separately. It includes an API reference and detailed discussions of various aspects of using Reliance Edge, including porting, building, configuring, and testing. This complete documentation, called the Developer's Guide, can be obtained for free from here:

In addition this README, see doc/ for a list of updates to Reliance Edge and a list of known issues. There is also a quick-start guide in the doc/ directory that describes step-by-step how to compile and run Reliance Edge in a simulated Windows environment.

Why Use Reliance Edge?

Reliance Edge is ideal for small embedded systems with data storage requirements, especially if there is a chance of sudden power loss or other system failures. Compared to “raw” disk access, using a file system like Reliance Edge removes the burden of tracking which sectors belong to which objects, and allows data to be updated more reliably. Compared to the FAT file system, using Reliance Edge eliminates the possibility that file system data will be left in an inconsistent state, corrupting the disk; Reliance Edge does not need a fsck/CHKDSK utility. Compared to journaling file systems, Reliance Edge has less overhead and results in less storage media wear for longer device lifetimes.

Reliance Edge uses a unique transactional model that not only prevents file system corruption but also allows a set of changes to be made in an atomic “all or nothing” fashion. This is very useful for applications that make sets of interrelated changes. By using the features of Reliance Edge, a set of changes can be incorporated into a single atomic transaction, which is committed in its entirety or not at all even if interrupted by power loss; this means the application does not need code to recover from partially-finished updates.


The typical hardware for Reliance Edge is a 32-bit microcontroller, but other targets are possible. In its typical configurations, Reliance Edge needs at least 4 KB to 5 KB of RAM, 11 to 18 KB of code space (on the ROM or NOR flash), and 500 to 700 bytes of stack.

Reliance Edge is not designed for high-end embedded systems that run complicated operating systems like Linux or Windows Embedded Compact. Embedded systems of that variety are better served by other file systems, like Datalight's Reliance Nitro.

Getting Reliance Edge Working

Before you can use Reliance Edge, it must be ported and configured. At a minimum, porting includes filling-in functions so that Reliance Edge can issue commands to your storage medium; depending on your needs, other functions may need to be filled in as well. These functions reside in a subdirectory in the os/ directory; see os/stub/ for a blank set of functions. Configuring includes creating a project directory (start by copying projects/newproj) and creating the two configuration files (redconf.h/redconf.c) using the Reliance Edge Configuration Utility (which can be downloaded from

These topics are covered in much greater detail in the Developer's Guide, linked above.

Using Reliance Edge

Using Reliance Edge is a simple matter of including the primary Reliance Edge application header in your application (either include/redposix.h or include/redfse.h) and compiling and linking against Reliance Edge binaries. The Reliance Edge driver must be initialized before it is used (via the red_init() or RedFseInit() functions) and then volumes can be mounted and file and directory functions invoked. The Reliance Edge API is documented in the Developer's Guide (linked above) and also via comments in the source code.


Reliance Edge is an open-source project licensed under the GNU General Public License v2 (GPLv2). Businesses and individuals that for commercial or other reasons cannot comply with the terms of the GPLv2 license may obtain a commercial license before incorporating Reliance Edge into proprietary software for distribution in any form. Visit for more information. The commercial distribution also includes extra tests and tools not distributed with the GPLv2 version.

See LICENSE.txt for the full license terms of this distribution of the product.

Getting Help

If you need assistance using Reliance Edge, and you have already consulted the Developer's Guide, contact

In the near future, a community forum or message board will be set up to facilitate discussion of Reliance Edge and allow users to get help from Datalight and from each other. In the meantime, please use the email address given above.


Contributions to Reliance Edge are welcome. Our policy is that Datalight must own the copyright of all code incorporated into Reliance Edge; if contributing a significant amount of code, you will be asked to file a copyright assignment agreement. See CONTRIBUTING.txt for further details and contribution guidelines.

To report bugs, please create a GitHub issue or contact