Hi Castro,
to set the concurrency in DP is not the complete story you have to keep in mind. Especially with Oracle backups you have to think about other parameters as well, like maxfilesperset, maxopenfiles, etc. Depending on settings like these, you want to configure the right amount of channels in DP. For Archive backups I recommend to stay with one channel (the allocate stuff in the backup specification), which means one drive with conncurrency set to 1. For online backups I often use 5 and more channels, depending on amaount of datafiles, if the instance is running on a RAC, etc.
However, keep in mind the whole stuff I talked about will complete change when you intend to use StoreOnce devices... There are special recommendations from the labs in Bristol available to archive the best dedup rate.
Best regards
Daniel