Repeating delta for missing records

Dear All,

We are frequently facing the issue wherein the unplanned downtime of the source system impacts the BI Delta Load(Delta records get missed upon re-pulling the delta). I checked the RSA7 queue, where there are two radio buttons when you display queue delta:

Delta                      

Repeat Delta

If I am not wrong, When the delta is pulled in BI it pulls the Data that exists when we select the radio button for Delta. I am not clear what exactly is the data that we get on selecting the button for repeat delta. Secondly please suggest how do we repeat delta in case of delta failure.

Regards.

Deepika