Backup/restore filesystem on ESP8266

[chemmex]

What's the best way to backup a filesystem image in order to flash it back via OTP? ESP8266 is 4M1M
Basically, I want to preserve current config

[TD-er]

You can use the Python esptool.py to read the entire flash.
This also supports an offset and size, so you could get a subsection of what's stored on the flash.
I think the file system starts at 3M and ends at 4M-12k (or 4M - 16k?)