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Description
The hot-backup feature (which is not released yet) is currently implemented without utilizing Erlang VM's async IO threads. I am not sure how long a LevelDB's LiveBackup() call can take so it will be safer to use the async IO threads to avoid blocking Erlang VM's scheduler threads too long.
http://erlang.org/doc/man/erl_driver.html#lengthy_work
As mentioned in the warning text at the beginning of this document it is of vital importance that a driver callback does return relatively fast. It is hard to give an exact maximum amount of time that a driver callback is allowed to work, but as a rule of thumb a well behaving driver callback should return before a millisecond has passed.