You should use the Google Cloud Storage gsutil command-line tool to transfer the data to Cloud Storage, and then use a batch processing pipeline to load the data into BigQuery. -> Correct. The gsutil command-line tool allows for broad compatibility and can upload data to Google Cloud Storage from a variety of sources, making it a versatile choice for a legacy system. From Cloud Storage, you have flexible options for loading the data into BigQuery or other Google Cloud services. This makes it both scalable and flexible for future analytics needs.
You should use a managed service like BigQuery Data Transfer Service to transfer the data. -> Incorrect. This service is primarily used for transferring data from supported sources like Google Ads, YouTube, and SaaS applications directly into BigQuery. It's not a general-purpose data migration service and might not be compatible with a "legacy system."
You should use the Google Cloud Database Migration Service to move the data to Cloud Storage. -> Incorrect. This is used for database migrations to Google Cloud's Cloud SQL. If the data needs to end up in BigQuery for analytics, this isn't the most direct or efficient route. Moreover, it moves data to Cloud SQL, not Cloud Storage, as the question suggests.
You should use the Google Cloud Dataproc import feature to import the data directly from the legacy system to Cloud Dataproc. -> Incorrect. Dataproc is a managed Spark and Hadoop service, which is more geared towards big data analytics and data transformation tasks. Importing data directly from a legacy system to Cloud Dataproc might involve unnecessary complexity and might not cover other types of storage or databases the legacy system might use.
https://cloud.google.com/storage/docs/gsutil
https://cloud.google.com/bigquery/docs