Hi bernard,
As already mentioned in the other thread please have a read of the MongoDB Limits and Thresholds.
Not taking performance into account - the limit for storing documents is set by the amount of disk space and RAM you have. The ability of MongoDB to scale out is only restricted by this.
Also have a look at MongoDB at Scale where there are some examples where users have grown from single server deployments to clusters with over 1000 nodes, delivering millions of operations per second on over 100 billion documents and petabytes of data.
Regards,
Markus