ShareGate Incremental Copy and Pre-Check: Delta Passes Without Duplicates

Direct answer: ShareGate's Copy-if-newer (incremental) mode copies new items and refreshes matched ones only when the source is newer — files by name, list items by title plus created date. Pair every wave with the pre-check gate, keep folder hierarchy mirrored, and use time-range filters instead of incremental for very large libraries.

Vendor note (October 2026): Option names and defaults change across ShareGate releases. Confirm current behavior in the official incremental copy, copy options, and pre-check documentation before your wave.

Part of the ShareGate series: start with the ShareGate migration tutorial, then continue to the mappings guide. Method references: Migration Validation and SharePoint Migration Checklist.

How matching works

An incremental pass first decides whether source and destination items are the same item, then decides whether the source is newer. Files are considered the same item when the file name matches inside the same library; list items when title plus created date match. Anything without a counterpart is copied as new. Anything with a counterpart is refreshed only when the source modified date wins — destination-newer content is left alone, which is exactly the protection you want during coexistence.

Two consequences follow. First, keep file names, titles, and created dates stable between passes — renames break matching and produce duplicates. Second, list libraries with non-unique titles need a unique key property configured, otherwise the matcher cannot pair items reliably.

The pre-check gate (every wave, not just pilot)

Run ShareGate's pre-check before each copy and treat red findings as a wave gate: fix connectivity, credentials, permissions, and configuration issues before the job starts, not mid-wave when rollback is expensive. A clean pre-check plus a frozen source window is the cheapest insurance a migration wave can buy.

Large libraries need a different tactic

Incremental mode crawls source and destination in batches to decide what to copy, so on very large libraries the comparison pass itself becomes slow or throttled. For those waves, use Copy-and-replace scoped by a time-range filter (items created or modified in your window) instead of a blanket incremental pass, and schedule the job for off-hours. Measure pilot throughput first so the schedule is evidence-based — see Microsoft 365 throttling and performance notes.

What incremental does not do

Three limits shape validation planning. Deleted-at-source items are not removed at the destination — that is deliberate data-loss protection, so plan a manual cleanup pass. Permission changes are not re-checked by the incremental pass — validate effective access separately per wave (permissions guide). And versioning behavior follows destination settings, with its own edge cases under high-speed import modes — sample version history explicitly rather than assuming it.

Choose the existing-item rule before the wave

In Automatic operation mode ShareGate applies your existing-item rule silently — the right default for bulk waves. Copy and replace overwrites same-named items and suits first-time loads into empty libraries. Don't copy existing items skips matches and suits top-up waves where the destination is already curated. Copy and keep both renames colliding files (folders merge instead) and suits merges where nothing may be lost. Copy if newer is the incremental delta described above. Manual mode prompts per conflict and is only practical for tiny pilots — never for bulk waves.

Duplicate-free delta routine

1. Freeze reorganizations — no folder moves or renames between the initial copy and the delta pass.
2. Pre-check green — all findings cleared, credentials and mappings confirmed.
3. Run the delta — incremental pass over the frozen source.
4. Reconcile exceptions — retry, archive, exclude, or manual-move per item with an owner.
5. Validate and sign off — counts, samples, permissions, links; owner acceptance recorded before the next wave starts.

Planning a ShareGate migration

If delta passes and validation evidence are where your program wobbles, bring the source, target, and timeline: Book a SharePoint Migration Assessment.

Continue with ShareGate Migration Tutorial, ShareGate Mappings Guide, and Migration Validation.