Lotus notes

Recently my notes server data base is down and the CEO has asked me what happen and i have explained to him from the pt of the hardisk failures to the pt of restoring the system files and user db.

Along the way, some user db will be restored as it is corrupted.

He ask how do we prevent this. I did told him we have 3 notes server (2 mta) and one notes server.

Can anyone advice me what other implementation should I do to make sure that if anything happen , the users mail will not be affect.