What protocol are you currently using (eg SMB/SFTP/rsync/etc)?
I have the current stable (v2009.10-2) TKL Fileserver and have over 1TB of files on it which is working fine (but all on one drive). I don't use Samba for uploads though, I use SFTP. And I rarely upload large amounts in one go since I set it up (although then I transferred 100s GBs onto the machine).
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