Before upgrading from XP to 7, I made backup on 2 external drives. I tested both backup, and they tested fine.
I then reformated my laptops hard drive & installed Windows 7. No problems were reported.
However I could not access the data on the 2 external hard drives. Windows 7 reported that they were unreadable and that I needed to reformat them!
The 2 hard drives were connected to my laptop when I installed Windows 7
I had to take both too a comuter geek who spent 2 days recovering my data - at a huge cost to me.
I am not impressed!!