Google Drive to SharePoint migration

Moving to Google is mostly a data-copy problem. Moving away from Google is a format problem. Native Docs, Sheets and Slides are not files in the conventional sense; they are documents held in Google's own representation and exported on demand. Every one of them changes format at the boundary, and formats that change can lose things: comment threads collapse into flat annotations, Apps Script bound to a Sheet does not survive, and complex Sheets formulas occasionally need review.

The second problem is links. Google-native documents cross-reference each other by Drive URL constantly. After migration those URLs still resolve to Google, which means a migrated document quietly points back at a tenant you are decommissioning. Link remapping is not optional; it is the difference between a migration and a slow-motion outage.

Google's shared drive membership model translates into SharePoint groups reasonably well at the top level. The exceptions are the items shared individually, outside any drive membership, and the anyone-with-the-link shares. Those links are the ones that matter for security, because they typically predate whoever is running the project.

We enumerate every external and link-based share before the move and produce a decision list: convert to a named SharePoint permission, convert to an organisation-scoped link, or revoke. Migrating a permissive share as-is is how an open Drive folder becomes an open SharePoint library.

Above roughly a terabyte, this stops being a weekend and becomes a programme. We move in waves by department, and each wave has a freeze window during which the source shared drive is read-only. The read-only step matters: without it you get edits landing in the source after the copy, and reconciling those by hand is miserable.

Throughput depends more on file count than total size. A terabyte of video moves faster than a hundred gigabytes of small Office documents, because per-file overhead dominates. We estimate on file count and use total size as a sanity check.

Nobody should switch off a Google tenant on the basis that a migration tool reported success. We run a three-part verification: file count and checksum comparison per library, a permission spot check across a stratified sample, and a link audit that confirms no migrated document still resolves to a Drive URL.

Only after all three pass do we recommend downgrading Google licences, and we recommend keeping a small number of archive-tier accounts for a defined retention window rather than deleting the tenant outright.