Onelake File Explorer Excessive Disk Space

Hello zzthatcher 

this is known behaviour of onelake explorer. 

OneLake File Explorer automatically syncs metadata for all files and folders that a user has access to in OneLake. This includes creating placeholders for files instead of downloading the actual data. While this approach minimizes bandwidth usage and prevents unnecessary file downloads, the cumulative size of metadata can become significant, especially when dealing with large datasets or numerous files and folders

https://learn.microsoft.com/en-us/fabric/onelake/onelake-file-explorer

Placeholder are lightweight representations of files that allow users to see the structure of their data without downloading it. However, frequent updates to metadata or placeholders (e.g., due to changes in the data lake structure or user access) can increase disk space usage over time.
3. Impact of Large Datasets: For organizations managing extensive datasets or lakehouses, the volume of metadata synced locally can grow substantially. This issue may be exacerbated if proper cleanup processes are not implemented for outdated or redundant data, leading to unnecessary accumulation of metadata.
4. No Automatic Data Download: It is important to note that OneLake File Explorer does not download actual file content unless explicitly requested by the user (e.g., by opening a file). This design ensures that disk space consumption is primarily due to metadata rather than full file downloads

Residual Metadata from Lakehouse Operations: If `OPTIMIZE` and `VACUUM` commands were not run consistently in the past, residual metadata from deleted or updated files might still exist in the lakehouse storage. Even after implementing daily cleanup routines, older metadata may persist unless explicitly purged with lower retention periods

Some workarounds 

Navigate to `%USERPROFILE%\OneLake - Microsoft` and manually delete unnecessary placeholders or temporary files if safe to do so.

Optimize Lakehouse Data
• Run `VACUUM` commands with a reduced retention period (e.g., 0 hours) to permanently remove residual metadata from deleted files.
• Continue running `OPTIMIZE` commands regularly to compact Delta tables and reduce metadata overhead

if this is helpful please give kudos and accept the solution