I have external HD, unfortunately files should be available also for Windows users, so I had to create ntfs partition. How does it work under my Gentoo? There is general problem that is impossible to create new files and folders even you have read/write support enabled in kernel.
On my laptop I got warnings like:
[ 1869.202693] NTFS-fs warning (device sdb1): parse_options(): Option utf8 is no longer supported, using option nls=utf8. Please use option nls=utf8 in the future and make sure utf8 is compiled either as a module or into the kernel.
To solve this problem helps ntfs3g:
lenovo / # emerge -av ntfs3g
lenovo / # ln -s mount.ntfs-3g mount.ntfs
Now you can connect your external HD over usb. Write mode should be fully enabled.