Forum Discussion
Lanceometer
Helper I
Helper IMirrored Snowflake Database Storage
Hi Folks, Some info upfront: - We use a Fabric F16 Capacity - I know the F16 Capacity offers 16TB free mirroring Storage I was trying the Mirrored Snowflake Database. It worked well. It was...
Hey Lanceometer ,
You have diagnosed it right, this is a source-side pattern, not a Fabric bug.
- Why storage grows: Fabric mirroring uses Snowflake Streams (CDC). A nightly full rebuild makes every row look new, so a fresh set of Parquet files gets written each cycle while older Delta versions stick around
- 1 day retention: It's only a threshold for when old files become eligible for cleanup, not guarantee that vacuum runs daily
- Manual VACUUM: Not supported on a mirrored database. Maintenance is handled internally (OPTIMIZE runs roughly every ~50 writes per table)
Next steps:
- Real fix: ask the Snowflake team to switch to incremental MERGE/UPDATE instead of a nightly rebuild
- Otherwise, skip mirroring for this table — use a OneLake shortcut or a pipeline load
- Keep retention at 1 day and give it a couple of cycles to plateau
Useful links:
Mirroring Snowflake in Fabric
VACUUM Delta tablesFound this useful? A quick Kudos goes a long way.
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LanceometerHelper I
Helper IThank you all,
yes apparently the problem is how the tables are updated in Snowflake via dbt.
I will sit together with our data engineers.
Until the the mirrored database is not an option for us due to our internal dbt build logic or until it is possible to vacuum mirrored dbs in fabric