SharePoint online site collection storage limit 25TB only and difficult automation ?

Hi Expeties, 

Everyone knows sharepoint site collection has limit of 25TB data, where there is one use case where I feel its failed or I would get proper answer from expert like you. So lets say if we use sharepoint online as document repository and external program (any which is not sharepoint) which would upload the documents 100TB data every year or more in sharepoint document library or teanant. how would external system know that sharepoint site collection limit has exceeded 25TB now put next data in another site collection, how would external system would know this ? how we can design to put data in sharepoint online tenant and retrive the data from sharepoint