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Most Cisco platforms don't directly support per-user/per-session rate limiting unless you define a policy for each user's IPs (which is a possible solution if we're only dealing with a hundred or so users).
6500s offer Microflow policing, which if you have that hardware, might be an option.
BTW, a possible alternative might be to use QoS to deprioritize FTP traffic to/from your DC FTP servers. Such a QoS policy allows such traffic to use all available bandwidth, but such consumption won't be adverse to more critical traffic.
Preferably I will never do that, you might be wasting your bandwidth inorder to achieve it.
It should be only required if all your users do FTP all the time. Now, again putting FTP is least priority queue is a smart solution, because you if at a time your whole pipe is empty or using very less traffic, then FTP will get more.
If your connection is chocked you will use only least assigned to FTP.