Airport Time Capsule - Shared disk with account - USB disk

I wonder why?

Because you did not first erase/format the disk......before.....you set up Accounts.....so permissions are all messed up.

The correct sequence of events would look something like.....

1) Move all the data on the current USB disk to another drive for safekeeping

2) Erase/format the USB disk that will connect to the TC

3) Set up Accounts on the USB drive connected to the TC

4) Move the data from the other drive back to the USB disk that is now set up with Accounts

Because the USB drive does not have the correct permissions.

In order for you to get the files on the USB to be seen by your account you need to actually copy the files again to the USB while plugged in and your account is accessed.

Didn't you see the warning that once you change over to accounts you will no longer be able to see any data on the TC disk or I presume the USB as well.

As a BTW there is very little actual security added by doing this.. since you just need to put the file access permissions back to device.. and all the files will be visible again.

It is more how easy it is to unset the permissions.. which means.. a person who actually has physical access to the TC can easily break in and change the permissions settings.. view all the files and recover it without leaving a trace. It is of course a home device.. and no more do you see its intention as a router with a hard disk for Time Machine backups as with trying to control permissions on it.

Either use a server like your suggestion.. but I think a better option.. albeit more expensive is to buy a Synology NAS.. which has a really simple but great interface.. lots of useful file server functions way beyond a TC.. and you can load it up with disks until your heart is content.

If you cannot afford one of the high end models.. consider using a HP microserver to which you can add whatever OS you like including Synology.. see xpenology.