I wonder how much of this is motivated by the lack of staff. The market of available mainframe operators has been drying up for decades. When your entire business depends on a technology nobody is willing to learn or go to school to understand, that creates a problem.
Also, from my understanding, it can take a tremendous number of distributed x86 systems to supplement the scale, speed and reliability of a mainframe. It's possible that unless FedEx gets away from managing storage arrays and hypervisor farms, they wouldn't have enough staff to operate the datacenters once they're full of enough servers to replace the mainframes.
> The market of available mainframe operators has been drying up for decades.
Just like many other industries, the market for mainframe operators that want to earn less than technologists in modern stacks has been drying up. A lot of mainframe operators refuse to bring their pay scales in line with what developers in modern stacks are earning. Why take a pay cut to go work on a 40 year-old system when you can work on modern stuff with more money?
They keep the pay low and complain about a labor shortage to deflect from the fact that they're simply choosing to ignore market forces.
Disclaimer: I have not worked directly on mainframes themselves.
They've been doing the same type of work for decades. Batch processing of records and transactions (payroll, insurance, banking, airline booking, etc.) IBM releases new mainframe models all the time, and typically companies will lease them and upgrade every few years.
When I worked at an insurance company, the mainframes were the core of their financials. They had around 8 of them in an active/standby DR site. The machines could do instruction-level error checking, meaning even a weird processor failure/error wouldn't impact the end transaction. Basically if you want to guarantee accurate handling of your money, you use a mainframe.
One common thing to see nowadays is the mainframe becomes abstracted by some other layer of API, such as a rest API. This has reduced the need somewhat for mainframe operators, but in the end you're still interacting with some COBOL that was written 30 years ago and somebody needs to understand it and the hardware. And the hardware is so different from traditional servers, you can't just pick it up and wing it. You really need someone who knows what they're doing.
Also, from my understanding, it can take a tremendous number of distributed x86 systems to supplement the scale, speed and reliability of a mainframe. It's possible that unless FedEx gets away from managing storage arrays and hypervisor farms, they wouldn't have enough staff to operate the datacenters once they're full of enough servers to replace the mainframes.