Can I reduce nvs_storage partition in the SoftSIM file system?

Environment

SIM type: SoftSIM
GitHub: nrf-softsim samples
Device: Nordic Semiconductor nrf91 Series

Question

Can I reduce the size of the nvs_storage partition in the SoftSIM file system?
Can I reduce the size of nvs_storage since it's not limited by TF-M like the other region?

Answer

You can try to reduce it but it is generally not recommended to go below 32 KB.

While nvs_storage is configured to take up 32 KB of memory due to TF-M flash region constraints, not all of this space is necessarily used.
You can repurpose unused space, as long as SIM-related data remains untouched.

For more details, check out Nordic’s NVS storage sizing guide.

Cause

The SoftSIM sample implementations for Nordic devices are designed to follow best practices for secure SIM storage using Trusted Firmware-M (TF-M).

Generally, reducing the nvs_storage below 32 KB may cause excessive flash memory wear. Based on our tests, 32 KB tends to offer the best balance between space and reducing flash wear.

TF-M Flash Region Constraints

TF-M enforces specific flash alignment requirements.
This results in a minimum flash region size of 32 KB for nvs_storage.
These constraints are structural, not indicative of how much data the SIM itself needs.

Developer Flexibility

The full 32 KB is not necessarily utilized by SIM-related operations.
If you're not modifying or overwriting the SIM data section, the remaining space within the nvs_storage partition can be used for custom application data or other non-critical storage needs.

More Information

To understand the underlying alignment rules imposed by TF-M, refer to Nordic's official documentation: TF-M Partition Alignment Requirements.

While you can't technically reduce the partition size below 32 KB without violating TF-M alignment requirements, you can make efficient use of the unused portion—just ensure the SIM data stays intact.