I don't really know where is the problem. Here are the facts :

- My Bitcoin QT is fully synced... I update it each 2 days approximately, and this sync takes 1 full hour... i expected a better speed, that's why I posted here.
- I have tested 2 HDD, and the problem stills the same. Both are Seagate Barracuda and have approximately 4 years. The first has 1 To, the other has 2 To.
- Slow reading only happen for Bitcoin QT (if I copy paste a big folder of, let's say, 10 go with multiple files, the average speed is 30 Mo/sec, with a min at 3 Mo/sec and a max at 120 Mo/sec).
- Both HDD haven't any issue, tested with GSmartControl.
- I'm not only interested in QT wallets, for security reasons and, btw, for fees reasons.

I'll test with another HDD, a Western Digital Green 2 To (4 years old too) and see if it performs better.