I had meant to add concurrently on the same box at the same time. My Solaris buddies had already informed me that with Sun's new line of T2000 servers, one can run Solaris, Unix and also Windows, while IBM can only support Unix and Linux, actually giving Sun more flexibility than IBM. This is fine (though I'm not sure why you'd want to run Windows on a T2000), but more importantly, they cannot run on the same box on different partitions. VMware for Solaris is only available on x86 systems. VMware ESX support will not run on SPARC. Xen on SPARC seems to be vaporware at this time, though Sun has been talking up 2007.
At present, to run multiple operating systems on a Sparc server, you can only do this with hardware partitioning, which is an inflexible model that allows their high-end servers to be divided into four-process partitions. There is also a concept of logical domains, which compliment Solaris containers, which will also be introduced in 2007 on their Sun Fire T1000 and T2000 servers. They will enable customers to run multiple operating systems simultaneously and are also supposed to complete Solaris containers to help improve efficiency and better utilize server capacity.
Part of the problem with Sun's future innovative strategies is that they continue to want to be all things to everyone. With up to 5 separate ways to virtualize, they will continue to confuse most people. IBM has one consistent strategy and method of virtualization. They also have only one hardware platform for their POWER5 technology. IBM gives you that flexibility. Sun does not. Certainly, Solaris has virtualization capabilities, though it's important to note that the focus is more on the initial configuration of like systems that on the dynamic control of resources within systems themselves.
Sun uses a system which is based on a concept called containers, introduced in Solaris 10. Containers allow many private environments to be created from within a single instance of a Solaris operating system. The containers are independent from the underlying hardware environment. Unfortunately, this method requires all partitions to have the same OS and patch levels. Their virtualization essentially virtualizes an operating system environment more so than hardware. In fact, they do not emulate any of the underlying hardware. The virtualized OS will make the calls to the hardware. That is where multiple partitions run on the same server, but with one kernel.
To reiterate, every operating system level must be exactly the same across all containers. One kernel fault will bring down every container. There is also limited security isolation as a result of single kernel across containers. What that means, is that one breach will impact every container in the OS image. Sun containers also cannot share I/O and that is not a good thing.
When configuring partitions, IBM has several ways including the use of their HMC as well as their new IVM, both of which are GUI-based. You can also script through the HMC using ssh. With Solaris, similar to partitioning and creating mirrors, one must type endlessly from the command line and when you type so many commands, you can make mistakes. You could use the Solaris Container Manager, though I suspect you will have similar problems that I have already had with the Solaris Management Console in configuring storage resources.
The strength of Sun's offerings is that it can run on multiple platforms, including Intel-based operating systems. Their virtualization is commonly referred to as lightweight virtualization. The advantage of this is that there is less overhead to traditional hypervisor-based solutions such as IBM's. Yet, the big disadvantage here is that you cannot have a diversity of operating systems. There is also no support for virtualization of hardware. When Red Hat came up with virtualization for RHEL5 (still in beta), they decided not to go the container route, and will introduce version 3 of Xen's hypervisor. The virtualization is a paravirtualized kernel; this virtualizes part of an OS operating environment and also selectively emulates hardware devices. It provides access to the native hardware. Of all the virtualization technologies out there, Xen most closely mirrors IBM's advanced Power Virtualization. But it is not yet available on the SPARC.
This was first published in December 2006