Reliance: Datalight's highly reliable embedded file system

The File System

for rapid development of reliable products

From consumer devices to tools for industrial testing and control, embedded devices may be treated with the utmost care or be dropped regularly.
Most embedded systems operate without the support of a plug in the wall, and they could be at risk for unexpected power loss. The rules and assumptions that apply to the PC environment are tossed out the window in the embedded world.

Reliance is a file system that was developed specifically for embedded systems. Engineers who choose Reliance do so because they cannot take a chance that data could be lost due to file system corruption.

Engineers use Reliance because:

• The file system is highly reliable
• The file system architecture is fast and efficient
• The file system is flexible and easy to use
• The file system supports any 32-bit operating system

How Reliance works

Datalight Reliance™ is a two state file system, the Working State and the Committed State.
Original data (the Committed State) is preserved until the new data (the Working State) is written and a transaction point is performed. During operation on the Working State, all file system modifications - including changes to directories, files and metadata - are stored on an area of the media that is currently unused and does not contain Committed State data. The possibility of corruption is eliminated because the data of the new transaction is written to an unused portion of the media. Writing to an unused portion of the media allows the previous state of the file system to be untouched. Valid data from the previous transaction is always available.

Transaction Points A significant event in the operation of the Reliance file system is the setting of a transaction point. When one or more file operations are successfully completed and data is committed to the storage media, a transaction point is set by the file system. It is at that moment that the file system changes from the previous Committed State to the new Committed State. The transaction point defines the state of the file system at the completion of one or more file I/O operations and remains the valid transaction point until the next transaction point is established.

Reliance Product Details

Unlike FAT-based file systems, Reliance™ offers developers the use of transaction points to ensure that directory information and user data are committed to media at regular intervals. Additionally, Reliance never overwrites needed on-media file structures or data. When a power glitch occurs, Reliance simply boots up and uses the last good Committed State, ensuring that a Reliance disk is always consistent.

Embedded devices that use Reliance are trustworthy and able to quickly boot.

Reliance is Highly Reliable

• Safeguards data in the event of power loss or other system crashes
• Transaction-based approach offers the user an "always consistent" file system
• Preserves both the file system's metadata and user data
• Transaction points are atomic - power loss at any point will not corrupt the file system

Reliance Architecture is Fast and Efficient

• A proprietary data format ensures reliability without sacrificing performance
• Reliance provides performance comparable to FAT-based file systems
• There is no need for a chkdsk utility or to check the integrity of the file system at boot time - allowing Reliance to offer a faster boot time compared to FAT-based file systems
• Unlike journaling or logging file systems, there is no ongoing recording of data - making Reliance more efficient

Reliance is Flexible and Easy to Use

• Works with virtually any block device driver, including those for flash memory, DiskOnChip, ATA, and SCSI devices
• Includes an automatic transaction mode so that no application changes are necessary
• Offers API functions that give the developer complete control over how transactions are performed
• Relianc is written in 100% ANSI C and ships in source code form

Reliance supports any 32-bit OS

• Ships as a drop-in replacement for the native file system under VxWorks, Nucleus, Windows CE and Linux 
• An RTOS Porting Kit enables developers to port Reliance to any 32-bit operating system
• Reliance is a "drop in" replacement for the FAT native file system and can be built into the bootable images 

Reliance development Specifications