no, it does not make a txt file on the disk. the mode disk just means that it will store the /log print on disk, instead of memory. for the user it just means that it will keep log after reboot. it does NOT mean that you will be able to download that file. we do no have a feature where it would make a downloadable log file. use syslog
yes, u can remote to your Log system to PC local one with MT sylog downloader program, u can download form MT download page first, than u can install to your local PC one that program default port is [514] than choice topic by remote action to [ip_your_PC]:514
than u can filter item as u like
if your logs system destination remote PC one, you has more space for your DISK at router, for me that action is better, i like it......