The flood alert kicks in when you try to write 10 MB of data...or possibly when writing less data really fast. I'm still testing to determine how long you need to wait before you can write again after the 9 or so MB is written (to avoid the flood alert).
EDIT: The limit is for every 5 minutes it seems. I'm able to write 9 MB per six minutes without running into it.
EDIT 2: Maybe not. In true Graal fashion, it works 4/5 times but other times it triggers the flood alert.
EDIT 3: Raising it to 11 minutes does not work now. Maybe the file activity of other servers also counts toward the limit? I have no idea

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