If there are multiple system dependencies either upstream or downstream, so that working in multiple systems during a staged migration would be untenable, then a big bang approach may be the only viable option from a change management perspective to minimize business disruption.
Although it can be painful to endure the downtime required for a single all-encompassing migration from the old to the new state, there are ways to minimize the pain and risk.
If it’s a large system, proper planning including dry-running, and a targeted cutover time with a detailed step-by-step cutover plan will be important to ensure that user access isn’t disrupted during critical times, and to guard against errors or gaps in the data in the new platform. Crucially, planning must include assessments of the quality and integrity of the data and any work that will be needed to clean this up, fill data gaps, and ensure that teams can confidently rely on it once using the new system.
Our migration technology makes it possible to perform an initial large migration, while shielding the data from users via appropriate security layers so that they do not access or use the migrated data prematurely.

Our migration software migration-center allows for the actual data transfer to be split into an initial large migration (pre cutover) and a subsequent second short migration phase with one or multiple deltas until the actual cutover migration, significantly reducing user downtime compared to custom solutions.
Once the first major initial transition has taken place, there will be an incremental cutover of any new or modified records. This delta option, which can include one or multiple subsequent delta runs, helps to minimize user downtime, confining the final cutover to a designated period such as a weekend or extended public holiday. By restricting the outage window, you can enjoy the best of both worlds – the clear-cut nature of a big bang migration, but with minimal business disruption as system usage is switched.