I don't remember that I have changed this value. I left it as it was.
Anyway I thought that this value defines the maximum amount of disk usage by MTA only and not by other processes. Can you please point me the documented explanation of this parameter? The second option you can choose is MB value(1024-default), and in conformity to your words it should say: after the use of 1024 MB (from all blades) MTA should stop working. I don't remember anytime when var/log was only 1024 MB used. May be I am misunderstanding... After all thank you so much for this hint!
The point is maybe I should then change this value to 20?. In this case I should have 20 from MTA and 55 from other blades and var/log will be less then 80% used.