if reading file on a partiton beyond 4GB works fine, is it safe to assume that writing will be ok too
Depends on how the file got there. If the file was written on a system which was >4GB-ready for sure and you just put the HDD into your system, then yes, if you can successfully read it, then it is safe to write to the partition, too.
But if you wrote the file on the same system you try to read it on, then it could happen that the file was written into the area below 4GB (destroying data on other partitons) and now is read from there, too.
Bye,
Thomas
