External USB Drive, write protected in EXT4 ???

Ok, so after having issues trying to use external USB disk to backup my ReadyNAS, i did some tests...

If I format the disk as NTFS, it works OK read/write.

It appears that if i format the disk as EXT4, i can't write on it, and can't change permissions.

Then i tried to format it as EXT3, and after half an hour it still didn't finished formatting. When i tried to eject the disk the ReadyNAS crashed.

After reboot, the disk disk was not even seen when i plugged/unplugged it... Ok, so i plug it on my Mac and format it as HFS+ then it is seen again on the readyNAS.

So, as HFS+, the disk is seen OK as read/write...

Then tried again to format as EXT3 and it took again ages to format... (so long that i didn't wait the end)

So, i will end using NTFS, even if it's a shame to use such format on a "linux" box...