Remember the Hanrahan Principle for IT Data Migration Projects

If you are ever running an IT Data Migration Project you should always remember the Hanrahan principle which will need a little of explaining for anyone who isn't British and older than 45.

The principle is that you should do checks on record counts in the source system and the target system to ensure they are explainable after the migration process. In some projects not all data will be migrated, it depends on the business requirements. But always check that the requirements have been well specified and met in test and live runs. So there should be counts of records that meet the migration requirements and counts of records which have been rejected because they don't meet requirements. The sum of these should match the total record count in the source system.

Why Hanrahan principle?

Brian Hanrahan was a BBC correspondent who is probably most famous for one quotation when reporting on the Falklands War in 1982. He was on the aircraft carrier HMS Hermes and was not allowed under Government reporting restrictions to say how many Harrier jump jets had departed on raids. However he wanted to reassure the public that there had been no losses. 

The clever phrase he used was:

I'm not allowed to say how many planes joined the raid, but I counted them all out and I counted them all back