How to optimize performance of backup process? Servers go down during backup
let us discuss few approaches for backup 


If you are using replSet then could be very easy to take backup from   secondary hidden if possible.It will simply makes things easy for you. 
3 member replica set 1 primary ,1 secondary ,1 secondary but hidden(can be used for backup)
you can use snapshot using LVM ,as it is system based approach so need manual intervention.for details Click here!
You can go for MMS(MongoDB Management Service) It will use your oplog to create backup.If not using replset then also you can create OPlog click here for details.


Also have a look at strategies comparison  click here