Its's works but a have a little inconvenient :
pbs1 ns1 backup : A, B , C, D
synchro every day on pbs2 with a bigger retention. --> pbs ns1 backup : A,, B, C, D, E, F, G ....
i wanted tu push back the backup ( G for exemple ) to PBS 1 , in order to have pbs1 ns1...