What happens to partially uploaded files?

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http://serverfault.com – Sometimes users would upload a very large file such as 10MB or so and it fails in the middle because one reason or another. My question is, what happens then? For example, if it fails at the 5MB mark - permanently failed because of failed internet connection, would it still take up 5MB of disk space? Where would the partially uploaded file be? How can I purge it? (HowTos)