Funny you should say that. Oracle is one of IBM's favourite marketing examples in favour of Linux on z/VM! Oracle is usually licensed based on the number of processors it runs on. IBM mainframe processors are among the most powerful on the server market; they have relatively low hypervisor processing demand because much of it is shunted to System Assist Processors that are not counted in Oracle charging; and some of the workload (e.g. Java and selected other work) can be shunted to specialty processors that are also not counted in Oracle charging. In fact, several very large enterprises have publicly shifted from Linux on x86 to Linux on z exactly because it saved them huge amounts of money in Oracle license fees. Oh... and they got hugely improved availability and security into the bargain, along with simpler systems management and reduced cabling, HVAC and power consumption.

Is the mainframe a dinosaur? Sure... and it's as agile and capable as the dinosaurs flying around our skies today*. IBM's z/VM operating system is the most reliable, most secure VM system on the market today, and it's got arguably the longest pedigree - it's been around for something like 40 years, cutting its teeth on government, academic and military workloads long before the internet was an everyday term. You can safely run up to hundreds of production and/or developer virtual machines in a single physical machine. Heck, you can run virtual machines within virtual machines! You can share multiple physical processors, memory and I/O almost effortlessly. You can cluster across multiple physical footprints, with full high availability to run active-active workloads if you need them for production or testing. (* NOTE: Over the last couple of decades, since around the time IBM's mainframes were declared dead like dinosaurs, archaeologists have discovered that dinosaurs are not dead at all: all of today's birds are clearly descended from theropod dinosaurs. Mainframes are similarly, um, not dead.)