Duplicate Rasters in Derived Mosaic Dataset after Synchronize Mosaic Dataset

[lah]

Hi everyone,

I'm running into an issue with duplicate rasters appearing in a derived mosaic dataset, and I’m hoping to get some guidance on best practices, specifically around the Synchronize Mosaic Dataset tool settings.

Environment / Setup

• Enterprise GDB (SQL Server)
• Orthomosaics (COG) stored in S3
• ArcGIS Pro 3.5.4 / ArcGIS Enterprise 11.5
• Daily ingestion python script

Mosaic Structure

• 3 source mosaic datasets, split by year (2024, 2025, 2026).
• Each source mosaic dataset grows to ~15,000–20,000 rasters.
• New orthomosaics are added daily.
• A derived mosaic dataset combines the three source mosaics using: 
  • Raster Type: Table
  • (following ESRI recommendations for scaling large collections)

Workflow

I have a script that:

1. Checks S3 for new orthos
2. Loads them into the appropriate source mosaic dataset
3. Runs Synchronize Mosaic Dataset on the derived mosaic dataset

The goal is simple:

 - Add any new rasters to the Derived MDS that were just delivered to the Source MDS. My Derived MDS should just be an identical, combined version of my 3 Source MDSs.

Problem

The derived mosaic dataset is accumulating duplicate rasters over time.

• There are no duplicate rasters in the source mosaics.
• This suggests that something in the synchronize process is reintroducing or duplicating items rather than strictly appending new ones.

What I've Observed

• Earlier, I had trouble getting the Synchronize Mosaic Dataset tool to detect new rasters at all.
• After adjusting parameters, it now detects them, but I’m now seeing duplication issues.
• Some parameters make the process take 8+ hours to complete - also not feasible.
• When testing on a smaller subset of mosaics (~10-20), I can't reproduce the issue.
• Here's what's running currently:

arcpy.management.SynchronizeMosaicDataset(
            in_mosaic_dataset=pDMDS,
            new_items="UPDATE_WITH_NEW_ITEMS",
            sync_only_stale="SYNC_STALE",
            update_cellsize_ranges="NO_CELL_SIZES",
            update_boundary="NO_BOUNDARY",
            update_overviews="NO_OVERVIEWS",
            build_pyramids="NO_PYRAMIDS",
            calculate_statistics="NO_STATISTICS",
            rebuild_raster="NO_RASTER",
            update_fields="UPDATE_FIELDS",
            fields_to_update="AquisitionDate;CenterX;CenterY;GroupName;ProductName;Raster;Shape;Tag;ZOrder",
            existing_items="IGNORE_EXISTING_ITEMS",
            broken_items="REMOVE_BROKEN_ITEMS",
            skip_existing_items="SKIP_EXISTING_ITEMS",
            estimate_statistics="NO_STATISTICS"
        )

Question

For this workflow, where I only want to:

1. Detect and add new rasters only to an existing derived mosaic dataset.
2. Not reprocess or duplicate existing rasters.

What Synchronize Mosaic Dataset parameters should I be using?

Otherwise:

• Is there anything specific to using derived mosaic datasets with the Table raster type that could cause re-indexing or duplication of referenced items?

Any guidance, examples of working configurations, or gotchas around Synchronize Mosaic Dataset in this type of architecture (Source MDS --> Derived MDS via Table Raster type) would be greatly appreciated.

Thanks in advance!