Read the long report by Slaughter and May (see top HN comment) with 250 pages of details, it is quite insightful and more than enough gory details. New archite

Read the long report by Slaughter and May (see top HN comment) with 250 pages of details, it is quite insightful and more than enough gory details. New architecture, new platform, implementation takes too long, migration and testing insufficiently planned and when push comes to shove even the too low non functional testing goals not reached but still gone live. With big bang approaches one has to keep in mind that complexity grows non-linear and at a certain size it becomes very hard. This migration was at a size that was getting hard but the approach taken and the way it was executed was clearly (see report) not on the level required. Big bang on smaller scale is the fastest and cheapest. Big bang on larger scale starts having big risks. A more incremental approach may have been better and cost effective with much lower risks. A honest cost comparison may have shown that - provided the big bang approach would have been properly planed with sufficient large scale integration, migration and proofing milestones and buffers for risks inherent in this one-shot approach.