What Google Cloud service does File Search Store use for permanent embedding storage?

I’m using Gemini’s File Search API for RAG. The docs mention embeddings persist indefinitely in a “specialized File Search database” with free storage, but don’t specify what Google Cloud service handles this backend storage (Cloud Storage? Firestore? Vertex AI Vector Search?).

Need this info to evaluate latency/availability and plan GCP integrations. Anyone know where to find File Search Store’s architecture details?