Hi Fernando,
I branched the new question to a separate one as your original question was answered.
For 2 MB in the threshold in the alert configuration, you would specify 2,000,000 as it takes a decimal value.
For equal to 0 MB or less than 0 MB, they would be 0 anyway. 0 MB is the same as 0 all around regardless of the unit MB, KB, GB, etc....
Thanks,
Matt