On Feb 10, 2005, at 1:27 PM, Doug Fairobent wrote:
Doesn't VMware on Intel provide the same advantage as z/VM when compared to discrete servers? In the case where there is no z/OS system (so that data sharing and communicating with z/OS are moot) why use z/VM instead of VMware?
Sort of.
VMware has much higher overhead than z/VM, because the x86 architecture was not designed with self-virtualization in mind. VMware cannot consolidate nearly as many servers onto a single frame as Linux under z/VM can. VMware does not provide nearly the level of granularity in terms of guest performance tuning that z/VM does. VMware's image management, though improving fast, is nowhere near what z/VM can do.
On the other hand, VMware is a lot cheaper and runs on much cheaper hardware. One of the best uses for it is actually not consolidation, but isolation of an application from the vagaries of the hardware. Upgrading a Windows server essentially means a total reinstall, first of the OS, and then of any applications, because the OS is so ridiculously dependent on stupid things like motherboard chipset, flavor of northbridge, and just what variant of the Pentium you've got. On the other hand, if you have VMware on the box, then when you upgrade the hardware you just reinstall the OS and VMware (which is a very simple app to configure) (we'll assume VMware ESX counts as both the OS and VMware for this case), and then fire up your VMware containers (and maybe increase their memory size--Windows CAN handle that without a reinstall) and you've just gotten the speed benefits of your upgrade, without having to mess with application configuration.
Adam
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