The archived data volume of ERA5 is about 1 Petabyte (PB) for the period 2010 to 2016 (11 Terabyte per month), including all parameters and level types. ERA5 is produced on an ongoing basis, so the data volume keeps increasing by another 11TB/month .
Please refer to the ECMWF retrieval efficiency documentation for best practices in retrieving ERA5 data.
IMPORTANT: Over 6PB of ERA5 data is expected by mid-2018, reaching near 10PB by end of 2018.
Downloading such large amounts of data is no longer practical nor possible for users. This is why the Copernicus Climate Change Service (C3S) is building up a climate data store (CDS), which will be equipped with a cloud based fast access storage. The CDS will be available by the end of Quarter 1 of 2018. The CDS will also provide a tool box to allow cloud-based data processing and reduce downloads. The most popular ERA5 data will be available through this cloud storage, thus avoiding most of the data access requests to the main archive, and improving hugely the system response to both data requests and downloads. In addition to this, the DIAS service (Copernicus Data and Information Services) will be deployed by the end of 2018. This will bring additional user functionalities to the CDS, in particular an environment for cloud-based user applications.
As data volumes grow so rapidly (higher time and spatial resolution, longer period coverage), the way forward is to bring users to the data rather than massive downloads of data by the users. Our service is simply not designed to cope with such huge downloads, and we cannot support them.