Thanks for your answer.
Can you tell me how I can configure or have an information a number of snapshot to retain?
I explain:
Now can I read the file : /etc/snapmirror.conf on the filer, I have this information:
120-122:h0 phfrru-sd122:mir_h0 - 02,22,42 7-21 * *
When I run the command : snap list , I see there are 2 snapshots retain for the snapmirror (h0 to mir_h0; snapshot retain at 13:02 and at 13:22). 
Volume mir_h0
working...
  %/used       %/total  date          name
----------  ----------  ------------  --------
  0% ( 0%)    0% ( 0%)  Aug 06 13:22  phfrru-sd122(0151728913)_mir_h0.43717
  0% ( 0%)    0% ( 0%)  Aug 06 13:02  phfrru-sd122(0151728913)_mir_h0.43716
  0% ( 0%)    0% ( 0%)  Aug 05 21:42  phfrru-sd122(0151728913)_mir_h0.43697 (snapvault)
Can you help me, how i must to do for increase or decrease the snapshot retain.