What's the difference whether or not to run PHP in safe mode?

help you fix your problem Your best bet is to use Write Concerns - these allow you to tell MongoDB how important a piece of data is. The quickest Write Concern is also the least safe - the data is not flushed to disk until the next scheduled flush. The safest will confirm that the data has been written to disk on a number of machines before returning.
The write concern you are looking for is FSYNC_SAFE (at least that is what it is called from the point of view of the Java driver) or REPLICAS_SAFE which confirms that your data has been replicated.

around this issue Is there anyway to make factory_girl create records in mongoid safe mode?? The original code is: , This trick may help. The following test passes:

      let(:user) { FactoryGirl.create(:user) }

      it "deletes a user" do
        user.new_record?
        expect { delete :destroy, :id => user.id }.to change(User, :count).by(-1)
      end

This might help you {safe:true} assures you that the callback function will get executed only after the insertion is done and {safe:false} does not guarantee that. I always use {safe:true}, just to make sure that I have the most up to date version of the DB.

this one helps. Take a look at Android Management API, seems more can't be done without custom device firmware.