% fortune -ae paul murphy

Scaring yourself and others

I pay Shaw cable for a static IP address, so it came as something of a surprise when they changed it - and worse, the changes this imposed at my end brought home the sad reality that I don't know Solaris as well as I thought: it took several rounds of things silently going wrong over the course of several days to discover that I'd sabotaged myself by breaking the link between the hosts and ipnodes files.

Finding out that something you normally treat as known background magic isn't, is frightening because it strikes at the heart of your self image as a competent professional in your field - and, of course, when others point this out to you the usual human response is to strike back in anger.

And that has a corollary: if you really want to scare yourself, pick something your bosses think they understand and force them into a position where they find out that they don't.

Halloween is a really good time for this - particularly if your bosses think virtualization is the answer to anything beyond their own need for budget management. People have finally started to catch on that there are performance costs to ghosting - the practice of running multiple guest OSes (or ghosts) under one real one.

In this context Sun blogger Jan Brosowski draws an interesting conclusion from a comparison between the results obtained from a SAP benchmark running under VMware and the same benchmark running on a similar machine in a Solaris container:

Do two "half-box" virtual machines on the same box perform better than the full box? Well, obviously no: Due to Intel's Hyper-Threading technology it's complicated to extrapolate from half of a system to a full utilized system. Both benchmarks used 8 virtual CPUs representing 8 of the totally available 16 threads, and not a single CPU. So they will have used 8 cores, but only the first thread of each.

Will the use VMWare mean a significant loss of performance?: Well, obviously yes. Of course, some of the lower performance is caused by the OS. We have already shown in several benchmarks the advantage of Solaris as OS for SAP. But - we speak about a lower performance of 36%, more than one third! So, there is a major impact of the virtualization.

Although containerization has much lower overheads than ghosting (because there's only one OS running) and his conclusion therefore makes intuitive sense, there are other issues that would have to be resolved before we could accept his conclusion as general - but if you just want to scare ghosting fans on Halloween, using this to show people selling PC virtualization as hardware efficient that it's arguably about a third less efficient than containerization should do the job nicely!

And if that doesn't suffice for you - try reminding them that their job is to provide the best possible user service, and that virtualization always reduces the quality of service by slowing system response.

Either way, you'll get your happy Halloween thrill - because their response? guaranteed to scare you first and them later!

Paul Murphy wrote and published The Unix Guide to Defenestration. Murphy is a 25-year veteran of the I.T. consulting industry, specializing in Unix and Unix-related management issues.