Forum Discussion

Lanceometer's avatar
Lanceometer
Helper I
1 month ago
Solved

Mirrored 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...
capacities
governance
one lake
  • Dev_Dholakia's avatar
    Dev_Dholakia
    1 month ago

    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 tables

    Found this useful? A quick Kudos goes a long way.

    Got what you needed? Marking this as the Accepted Solution helps others land on the right answer faster when they search for the same thing

Dev_Dholakia's avatar
Dev_Dholakia
Resolver IV
1 month ago

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 tables

Found this useful? A quick Kudos goes a long way.

Got what you needed? Marking this as the Accepted Solution helps others land on the right answer faster when they search for the same thing