When you see this message in /proc/mdstat, it means that the raid partition is in auto-read-only mode. This mode is set when the device has not been written to since the last check.
In case of a normal partition, just try to write a file and the mode should disappear.
When its a swap partition, you can use this commands:

I got a cron email with this content, so i started investigating:

It seas about a Warning (W:), but i think it should rather be a notice…