I have attahed 3TB USB drive - it was recognized and formatted ok.
I have recorded a few broadcasts on it, and I removed a few of them, which also seems to work.

TV has been powered off and on

Now, the HDD is constantly active while viewing a broadcast (not recording or anything!).
If I enter SmartTV and the internet browser, the HDD stops -- but starts again immediately when I exit back to watching TV broadcast.

So what's it doing on the HDD -- filesystem check?

TV: 55pfl8007T/12 - fw 150.82