WiFi.MSC – A USB device to securely access storage over SSH

Summary

This is firmware that can be configured and loaded onto an Espressif ESP32-S2 or ESP32-S3 to create a USB mass storage device, whose data is accessed over WiFi via SSH using key authentication. It is based on the LibSSH-ESP32 library.

Author

Created by Ewan Parker https://www.ewan.cc/ on 16th September 2023, and initially released on 19th September 2023.

Use Cases

A small USB bus powered device that offers up to 8 TB of storage. Simple alternative to iSCSI over USB and WiFi. Shared access to USB storage (read-only or filesystem dependent). Remote adhoc access to administered storage. Flexible boot media. NAS on-a-stick. Cloud storage accessed from anywhere over a cellular WiFi hotspot.

Limitations

Slower than local storage. Cached data transfer speed reaches 980 kB/s on the ESP32-S3 and 580 kB/s and higher for the ESP32-S2. Network speed measured to be about 61 kB/s on an ESP32-S3 and slightly slower on an ESP32-S2. No error checking implemented (yet). Needs WiFi and SSH access when started and without interruption. Single storage profile hard-coded into device firmware. To change the profile the SPIFFS (or entire flash) must be wiped and the firmware rebuilt and re-flashed. No status/activity feedback or user interface. No Ethernet support. Memory is tight on the ESP32-S2.

Configuration

Run the config/create_config.sh script. Leave the passphrase blank. Edit the files now created in the config/data/0 directory Re-run the config/create_config.sh script to fix-up any changes you made to the configuration. Two files are created: wifimsc_disk_config.h and wifimsc_ssh_config.h. If not already present, copy your SSH key to the remote SSH server, e.g. using ssh-copy-id -i. Build and uploaded the firmware using arduino-cli or arduino-ide. Enable PSRAM first if you want caching.

Usage

Plug the device into any USB host (e.g. PC). It will take a few seconds to connect to WiFi and create a session over SSH. Then the storage will become available. The first time the device is started it will create the backing-file using the SSH credentials on the remove host (defaults to /var/tmp). The backing-file can also be accessed and administered locally using all standard tools such as mkfs, mount, cp, etc.