🥉Bronze Layer

NEW

Also known as: Raw Layer, Stage 1

The raw data layer that lands source data in its original format with minimal transformations.

DESCRIPTION

In medallion architectures, the Bronze layer is the entry point for raw data ingestion. It preserves original fidelity, including duplicates and schema quirks, enabling reproducibility and audit. Typical operations include landing, basic parsing, and metadata capture, but not heavy cleansing. Storing data append-only with lineage supports replay and downstream correction. Access is usually restricted, with Silver and Gold layers providing curated views. Bronze facilitates schema evolution by isolating upstream variability.

ALTERNATIVE DEFINITIONS

Databricks

The bronze layer contains raw data ingested from various sources in its original format.

Defines Bronze as the raw, original-format landing zone in medallion architecture.

Source

Databricks Glossary

In the medallion architecture, the bronze layer is the raw data layer, where data is ingested and stored with minimal transformations.

Highlights minimal transformation and ingestion focus.

Source

Delta Lake

Medallion architectures commonly organize data into bronze (raw), silver (clean), and gold (aggregated) layers to progressively improve data quality and structure.

Positions Bronze within the progressive layering pattern.

Source

RELATED TERMS

Medallion Architecture Data Lake Delta Lake Schema-less Data Ingestion Lineage Data Validation Gold Layer Governance

COMPETING TERMS

Silver Layer

RELATIONS

• Broader: Layer

KNOWLEDGE AREAS

Data Engineering Data Architecture Data Management Data Warehousing & BI

TARGET AUDIENCE

Data Engineer Data Architect Analytics Engineer Data Steward

EXTERNAL SOURCES

• Wikipedia - Delta Lake
• Databricks - Official medallion architecture guidance
• Delta Lake - Resources on lakehouse layering

TOP QUESTIONS

Why keep data raw in the Bronze Layer?

Raw storage preserves provenance and enables reprocessing with new logic, avoiding irreversible transformations early in the pipeline.

Category: Relevancy

What operations are typical in the Bronze Layer?

Landing files, basic parsing, metadata capture, and append-only writes; heavy cleansing is deferred to Silver.

Category: Practice

What are risks in the Bronze Layer?

Exposure to PII and malformed data demands tight access controls and robust metadata management.

Category: Risk

How does Bronze Layer support lineage?

By preserving original records and schemas, enabling traceability from curated downstream datasets back to raw inputs.

Category: Management

Is the Bronze Layer schema-on-read or schema-on-write?

Typically schema-on-read, capturing raw formats while recording schema metadata for later interpretation.

Category: Opinion

How does the Bronze Layer interact with CDC streams?

It can land CDC events append-only, enabling accurate downstream reconstruction of current and historical states.

Category: Example

What storage suits the Bronze Layer?

Object storage with transaction support (e.g., Delta Lake, Apache Hudi) aids reliability and replay.

Category: Tools

How to secure the Bronze Layer?

Implement least-privilege access, encryption, tagging of sensitive data, and strong audit trails.

Category: BestPractices

What is an alternative to a Bronze Layer?

A single-zone lake can work, but layering improves governance and quality progression.

Category: Alternatives