# Partition Field Immutability and Merge-Delete-Recreate Migration > Source-anchored research for Partition Field Immutability and Merge-Delete-Recreate Migration. Run status: COMPLETED. Parent: [Online Archive partition-field selection](https://llms-explorer.com/tree/online-archive-partition-field-selection/) · 3 facets · 11 facts · page: https://llms-explorer.com/tree/partition-field-immutability-and-merge-delete-recreate-migration/ ## Structure and components - Atlas does not support modifying an existing Online Archive’s partition fields or structure through its UI or API. Treat a partition redesign as archive replacement. (high confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/manage-online-archive.md) - MongoDB’s replacement procedure rehydrates archived data into the Atlas cluster using $merge, then deletes the old archive and creates a new archive with the desired partition fields and structure. (high confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/manage-online-archive.md) - Editable archival age limits and custom filter expressions do not imply editable partition structure. Atlas also disallows switching an existing rule between Date Match and Custom Filter. (low confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/manage-online-archive.md) ## Problems, failure modes and limitations - Verify restored data on the Atlas cluster before deleting the old archive. Atlas automatically deletes archived files and metadata five days after archive deletion; that deleted data cannot be restored. (medium confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/manage-online-archive.md) - The Pulumi resource documentation warns that some fields are immutable after creation and identifies ONLINE_ARCHIVE_CANNOT_MODIFY_FIELD when correcting an invalid dateField would require destruction. This warning does not establish automatic preservation or repartitioning of existing archived data. (low confidence) (verified as of 2026-10-14) — [source](https://www.pulumi.com/registry/packages/mongodbatlas/api-docs/onlinearchive/) - In the Crossplane v1.4.1 schema, the explicit immutable warning belongs to dataProcessRegion. partitionFields exposes fieldName and order but supplies no in-place migration procedure; the region warning must not be misquoted as partition-field-specific evidence. (low confidence) (verified as of 2026-10-14) — [source](https://marketplace.upbound.io/providers/crossplane-contrib/provider-mongodbatlas/v1.4.1/resources/mongodbatlas.m.crossplane.io/OnlineArchive/v1alpha1) - Deleting an archive schedules deletion of its storage files and metadata five days later; after that deletion the archived data cannot be restored. (low confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/manage-online-archive.md) ## Facts and statements - The restoration procedure requires pausing the associated archive and connecting with its Archive Only connection string before running $merge into the Atlas cluster. (low confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/restore-archived-data-with-merge.md) - Provision enough Atlas cluster capacity for the restored data. MongoDB cautions that the granular $merge restore approach is not recommended for datasets around 1 TB with many partitions. (low confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/restore-archived-data-with-merge.md) - The documented $merge example keeps an existing matching cluster document and inserts unmatched archived documents. Multiple on fields require a compound unique index on those fields; duplicate archived _id values need explicit consideration. (low confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/restore-archived-data-with-merge.md) - Before restoration, pause the associated archive and connect through its Archive Only connection string. Verify the restored documents in Atlas before deleting the old archive. (low confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/atlas/online-archive/restore-archived-data-with-merge.md)