I delivered a complex, highly customized enterprise back-office system for a large Fortune 500 some time back. It involved a handful of servers (all as VM's), x3 to accommodate DEV/QA/PROD staging.
It worked great in volume testing in our environment. Their IT department installed it on high end servers (hundreds of cores, incredibly expensive storage subsystems, etc) but users complained of latency, random slowness, etc. IT spent weeks investigating and swore up and down it wasn't their end and must be a software issue. We replicated and completely sanitized production volumes of data to try and recreate locally and couldn't.
Finally I flew down and hosted their entire infrastructure off my laptop for a day (I'll skip all the security safeguards, contract assurances, secure wipes, etc). It flew like a thoroughbread at a racetrack. No latency, instant responsiveness, no timeouts, no hiccups. Their entire staff raved about the difference. The results gave the business unit VP what she needed to bypass the usual, convoluted channels, and someone must have lit a fire under their IT VP - by the end of that day their internal techs identified a misconfiguration on their storage arrays and solved the problem. I can only guess how many other apps were silently suffering for weeks or months on the same array. I joked I'd be happy to sell them a laptop or two for a fraction of their mainframe cost.
