AEO Primer · 4 min read · May 2026
What is OneLake? The Tenant-Wide Storage Layer Inside Microsoft Fabric
By Thinklytics Partners, Practitioner Notes
OneLake is Microsoft Fabric's tenant-wide unified storage layer, built on ADLS Gen2, with a single namespace and shortcut features that let Fabric reference data in S3, ADLS, or Dataverse without copying.
Topics covered
- OneLake
- Microsoft Fabric storage
- ADLS Gen2
- Delta Parquet
- OneLake shortcuts
- OneLake vs ADLS
- Fabric storage
Frequently asked questions
What is OneLake in one sentence?
OneLake is Microsoft Fabric's tenant-wide unified storage layer, built on ADLS Gen2 under the hood and addressable via a single tenant-wide namespace, with a shortcut feature that mirrors data from S3, ADLS, or Dataverse without copying.
Is OneLake different from ADLS Gen2?
OneLake uses ADLS Gen2 storage primitives but presents them as one logical namespace per Microsoft tenant. ADLS containers are still there under the hood, but the access pattern, security model, and shortcut feature are Fabric-specific. Think of OneLake as ADLS with a tenant-wide front door.
What file format does OneLake use?
Delta-Parquet by default. OneLake stores tabular data as Delta Lake tables (Parquet files with a transaction log). It supports reading external Apache Iceberg tables via Fabric Mirroring in 2026, but writes still target Delta. Teams that need true Iceberg portability across Snowflake and Databricks typically standardize on external Iceberg tables.
What are OneLake shortcuts?
Shortcuts are pointers from one OneLake path to another storage location (S3, ADLS, Dataverse, another OneLake region). The shortcut presents the external data as if it lived in OneLake, with no copy and no scheduled refresh. Egress costs and latency apply when querying through the shortcut.
Do I still need ADLS containers?
For Fabric-native workloads, no. OneLake replaces the per-workspace ADLS containers Synapse used. For non-Fabric Azure workloads (Azure ML, Azure Databricks, custom Azure services), ADLS containers are still the right primitive. Most organizations end up running both during the transition period.
How is OneLake billed?
OneLake storage is billed separately from Fabric capacity. Storage is roughly $0.026 per GB per month for hot data in 2026 (similar to ADLS Gen2 pricing). Caching for Direct Lake mode is included in the Fabric capacity cost. Shortcut traffic does not add storage cost but can add egress cost when crossing clouds or regions.
What workspaces structure should I use in OneLake?
One workspace per logical domain (Sales, Finance, Operations, Engineering, etc.), with workspace-level permissions held by the domain owner. The default of one workspace per team creates an access-control mess at 8+ workspaces. The medallion layout (bronze, silver, gold) typically lives as folder prefixes within a workspace, not as separate workspaces.
How does Thinklytics work on OneLake architecture?
OneLake namespace strategy, shortcut design, and workspace partitioning are part of our 4-week Fabric current-state assessment. See [Microsoft Fabric data engineering](/insights/microsoft-fabric-data-engineering-2026) for the full architectural pattern we recommend.