English to French Art/Literary General / Conversation / Greetings / Letters article sur l'nformatique (la consistance éventuelle)

The context: At the foundation of Amazon's cloud computing are infrastructure services such as Amazon's S3 (Simple Storage Service), SimpleDB, and EC2 (Elastic Compute Cloud) that provide the resources for constructing Internet-scale computing platforms and a great variety of applications. The requirements placed on these infrastructure services are very strict; they need to score high marks in the areas of security, scalability, availability, performance, and cost effectiveness, and they need to meet these requirements while serving millions of customers around the globe, continuously.

Under the covers these services are massive distributed systems that operate on a worldwide scale. This scale creates additional challenges, because when a system processes trillions and trillions of requests, events that normally have a **low probability of occurrence** are now guaranteed to happen and need to be accounted for up front in the design and architecture of the system.

The article appears on a computing blog. I would like to translate it thus:

Cette échelle crée des défis supplémentaires, car quand un système traite des trillions et des trillions de requêtes, des événements qui ne se produisent que rarement sont désormais certains de se produire, …

However, my (French) client prefers me not to stray too far from the original text, and I have a feeling he would prefer something like:

Cette échelle crée des défis supplémentaires, car quand un système traite des trillions et des trillions de requêtes, des événements qui ont une probabilité de fréquence faible, ...

OR

... des événements qui ont une probabilité de survenue faible, …

Do either of these latter versions sound acceptable to French readers? Thank you for your help.