Here are the most common migration strategies that are performed:
Big Bang Migration:
A single pass migration strategy that will move the entire mailbox in one pass after MX records are cutover.
A typical scenario consists in cutting over on a Friday evening and migrating during the weekend.
- Simplest to implement.
- Migration may potentially not complete in time for various reasons.
- Users accessing the new system may not have access to all their data when work resumes.
- Any items created during or after the migration may be missed by a single pass.
- Downtime may occur for some users if migration fails or takes too long.
A multi-pass migration consists of pre-staging a majority of the data prior to cutover and doing a Full (Delta) Pass after cutover.
- Majority of data is available at time of cutover.
- Mitigate migration risks in which the majority of data will be available regardless of availability of source server at time of cutover.
- Will not propagate updates, deletes, or moves of the items previously migrated in the first migration pass.
A quick-switch migration consists of pre-staging only the newest emails. New emails are accessible immediately at time of cutover by users and the remaining data is backfilled over time.
- Initial migration is quick.
- Time between cutover and data availability is short.
- Not all data is available at time of cutover for end users.