I configured this in RB433UAH:
-------------------------------------------
/system logging action
add disk-file-count=200 disk-file-name=usb1/logdarsemaggio disk-lines-per-file=10000 disk-stop-on-full=no \
name=darsenalog target=disk
/system logging
add action=darsenalog disabled=no prefix="" topics=account
---------------------------------------------
It works well for log account on 4Gb pendrive. When you restart routeboard to power failure, the log does not work anymore. We must change the file name (log) to work!
Solution? Script?
Thanks

Thank you very much for the problem.
Other user reported the same problem some time before, the problem will be fixed in the next MikroTik RouterOS version (for both v4.x and v5.x releases).

UUUHHHHHHAAAAAAA

Hello,

I know this is a very old post but I've got the same problem now in 6.1 on a RB2011UAS-2HnD.

After reboot i need to change the file names when logging to a USB drive.
After the change the logging starts to work again.

if you suspect a bug, better submit it to support, it might get lost in the forum