The disk space problem is still a problem to machines running FTP service.
The easiest and most efficient way to enforce disk quotas on the FTP server
machine is to enable them in the operating system, just as you would for
a regular login account. The big problems with this are that not
all operating systems have quota support built-in, and for those that do,
only real users listed in the /etc/passwd file can have them.
If your system has operating system quotas and you only allow logins from
real users, you should use the existing quota system. Otherwise,
if your OS doesn't have quotas or you want virtual users to have a disk
quota, you can use NcFTPd's built-in (as of version 2.5.0) support
Naturally NcFTPd avoids doing that very system-intenstive calculation until it needs to. Under normal circumstances, this calculation is not done until something that would increase disk usage would occur (these are: file uploads, directory creation, or symbolic link creation). If you choose to display the quota status to the user, then this also causes the disk usage calculation to be done. Therefore, you should resist the temptation to put the quota status in the login message, since that would mean that each and every login would cause the disk usage calculation to run, whether or not they do an upload.
Also think twice before using NcFTPd quotas over an NFS partition.
The disk usage calculation will be much slower than it already is on a
local hard disk.
They should also use an FTP client that displays the messages from the FTP server; otherwise when the user exceeds quota you'll get unnecessary calls because their uploads are failing but the client program did not bother to tell them that it got a "disk quota exceeded" message.
The users could also benefit from an FTP client that can issue the "SITE QUOTA" command to display their current disk usage. Another way to let the user be aware of their quota is to put that information in the login message or logout message using special NcFTPd cookies in the message text (described later). Again, this depends on the user having a client that displays this message!
The end result is that if you use quotas, you should tell the users
how to check their FTP quota, and if they get errors related to uploading,
that it could be because they have exceeded their quota.
The user can simply close a FTP session and reconnect to get a more accurate quota calculation.