Google Cloud Storage is Google's object storage service for unstructured data, such as files, backups, media and the raw files of data lakes. Data is kept in buckets and accessed through an API. The customer chooses where each bucket is located: in a single region, a dual-region, or a multi-region, including the EU and US multi-regions. The service is delivered as a cloud service through Google Cloud.
Google LLC is a subsidiary of Alphabet Inc. and is based in Mountain View, California. US legislation such as the CLOUD Act can therefore apply to data that Google controls, whatever the location of the bucket. Google's Data Processing Addendum states that Google acts as a processor under the GDPR and the Swiss FADP. Customers who choose the EU multi-region have objects stored in data centres in EU member states; the London and Zürich regions are excluded. The product is not open source and cannot be self-hosted, so organisations that want full control over their infrastructure have to weigh that against a sovereign provider.