Its not. They don't store the raw IP packet data, instead they store the metadata (this was revealed in a leak a long time ago), like the type in this article (

Its not. They don't store the raw IP packet data, instead they store the metadata (this was revealed in a leak a long time ago), like the type in this article (data source and destination, timestamps, size of the data, etc.) the metadata is orders of magnitude less data than the raw packets and likely easily compressible, so I wouldn't be surprised if they keep it all for a decent chunk of time.