Basic USB disk sharing is possible in the 7501, though not with the stock firmware. Install Lemonade to enable it, or manually install it yourself. The implementation in Lemonade uses ftpd (via tcpsvd) provided by Busybox 1.17.1.
Once Lemonade is installed and the router is restarted, a basic, anonymous FTP file sharing service will be available at
Note that this is an anonymous setup, with no security. It is simply for sharing files within a home or small office setup, and provides no privacy. As such, it is still suitable for uploading image, music or video files to the media directory. It is not intended for storing or sharing any confidential or critical files, nor is it designed for sharing over the WAN (to the internet).
The interface for it is simply drag-and-drop, for most FTP clients. Some ideal clients for this are:
1. Maximum (theoretical) filesize is about 4GB. This is because the USB drive must be formatted vfat. This is something that is kernel-dependent, and we cannot "code our way around it", to the best of my knowledge. To be honest, I wouldn't try to put anything that large on this type of storage. This unit is not really designed to be a heavy duty NAS device.
2. In vfat, symlinks are not possible. This is because of vfat, again.
3. Anyone on your network can get access to the USB share - it is not a secure share.
There is an ext2 module here that you can experiment with. If you load it, it may allow you to use an ext2 filesystem. I have not tried it, and I'm not very interested in it since it is not a journaled fs.
Also, you could experiment with authentication or another FTP server.
*The Finder in 10.5 and 10.6 seems to be limited to read-only access. It seem that this is not a bug in Apple's implementation, but rather they designed it that way.