If you set attachments to be stored in the file system instead of in the database, this is already done.
Files are not stored on username, but on userid.
For example if your attachment base-dir is set to 'forum/files', and a member with userid 123 uploads an attachment (picture, zip file or whatever), this file would be stored on the server in the directory:
'forum/files/1/2/3/'
Files are placed in subdirectory names made up from splitting all the number from the userid.
So member with userid = 98, would use directory:
'forum/files/9/8/'
|