Replacing sensors / actuators (followingly called IO-Link devices) is a common scenario in the field. Replacement needs to be done fast, with minimal machine downtime and without need of personell with expert knowledge.

Using IO-Link devices makes device replacement easy and comfortable thanks to the backup and restore functionality - called Data Storage (DS) - available in IO-Link.
There are several names out in the automation world for the same feature:

• Data Storage
• Backup and Restore
• Parameter server
• Device replacement

Data Storage functionality

Replacing an IO-Link device requires, obviously, the replacement hardware, and the application specific parametrization of the device.
This application specific parametrization is what the IO-Link master is able to store in his "stomach" - the Data Storage.
Once this feature is activated in the IO-Link master you can choose of different master behaviors:

NONE
No backup of the device parameters is made in the master.

BACKUP/RESTORE
The master stores the parametrization of the connected IO-Link device (initially automatically) and is ready to restore it in case of device replacement.

RESTORE
No automatic backup of the device parameters is made in the master. Manually initiated backups are possible. The master monitors the port and restores the parametrization if a replacement device is detected.

Info

The setting to enable the DS / backup and restore feature is different in every IO-Link Master.
You need to consult the corresponding operation manual of the IO-Link Master your choice to get the instructions how to enable it.
Here you see an screenshot of the webserver user interface of SIG350 from SICK.

Validation

Additionally (so also useable if DS is not used - example see screenshot above) and in connection with the DS functionality is always the 'Validation' feature.

If you replace a device - of course - you have to make sure to replace it by a compatible device. For this reason the DS functionality includes a check for the correct device.
This is done by comparing the Device ID and the Vendor ID of the connected product with the ID values in the DS.
For details about Vendor ID and Device ID please read a separate article linked below.

If the IDs match with the IDs stored in the backup of the master the master will carry on and compare the parametrization if the device with the one stored in his "stomach".

If not there will be an error event to inform the above communication layers about the mismatch:

Source: IO-Link Interface and System Specification V1.1.3, June 2019

Backup

Depending on your setting of the data storage behavior (BACKUP/RESTORE) the master creates the first backup of the application specific parametrization automatically. 
If all settings are already correct on the device you are done

But most of the time adaptions are necessary. Then you need to update the content of the data storage.
Or you chose RESTORE only behavior. Then you need to create the update manually in any case.

There are different options for parametrization of IO-Link devices. Thus also different ways to update the data storage content.

DS update possibilities

Parameter changes on the device itself (display, buttons, potentiometers, etc.)

All changes done directly on the device are reported automatically to the IO-Link master. The IO-Link device will inform the master about parameter changes and the master will update it's data storage accordingly.
Attention: In RESTORE only mode no update is carried out!
 

Parameter changes via PLC (as well SICK function blocks) or other programming tools

If PLC programs or other application specific processes access the device via the IO-Link interface and modify parameters no automatic action is done.
The user program needs to take care for the update of the data storage content after the adaptions has been done. Also the function blocks offered by SICK to simplify service data exchange to not trigger any data storage updates.
To do so system commands are available to control the data storage functionality.

If you like to resume the changes done by PLC communication in the DS the IO-Link device needs to signalize this to the master using an IO-Link Event.   
This event is produced by the device if it receives the System Command “ParamDownloadStore” (value 0x05).
→ To resume new parameters write an ISDU with value 0x05 to the System Command ISDU (index 2) at the end of your sequence.
 

Engineering tools, like SOPAS (Off-site commissioning)

Engineering tools are obligated to set the DS upload flag after parametrization has been finished using their graphical user interfaces.
This is true for engineering tools using the IO-Link interface itself (Attention: new since V1.1.3) and also if additional interfaces like TCP/IP, USB are used.
→ Since engineering tools didn't behave like that before IO-Link interface version V1.1.3 monitor carefully if your IO-Link master updated his DS content when the IO-Link device is connected back to the IO-Link Master!