Why Virtualize? Part1


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Since the explosion of interest in Host based virtualization products like VMware, Zen and Microsofts Hyper-V, it seems like the IBM concept from the 70’s mainframes has really hit home. I remember sitting in on a very early customer focus group when we are mid-development of SVC and the speaker was discussing how virtual memory is taken for granted today, you don’t really think about your pagefile. The speaker went on to describe his vision for storage virtualization, the names are the same because the concept is the same. Abstraction. Let one part of the system think its using another part when really its something totally different. The speaker went on to explain that he felt Storage Virtualization would become the same, i.e. something you take for granted. So why would we want to do that? Well thats what I plan to outline over the next few (probably weeks) of posts – unlike Tony who manages to nicely week’ify his topics, I seem to manage a month’ify at best!

My initial thoughts are to cover the following ideas :

  • The problem
  • The solution
  • The benefits
  • The gotchas
  • The things to look for in a solution
  • Performance Considerations

This list is likely to change as I write, and get feedback but thats where I’m heading over the next few weeks – feel free to ask for any thoughts, topics or content and I’ll do my best.

As an aside, Windows pagefiles… Most of your are probably using some flavour of Windows to read this page, if you are, where is your pagefile? Have you thought about it recently? Probably not, most likely you have left Windows to create it itself, manage it itself and then complain when your hard drive starts thrashing.

One of the great un-features of Windows is that is can’t defrag ‘unmovable’ files i.e. the pagefile, the registry and your hibernate file if you have one. Ok so page defrag is a great util from what were SysInternals, which Microsoft bought up! (Says a lot!) Anyway, the best solution I’ve found is to always create a small partition that is just over double the size of your memory (by about 256MB). Once you’ve then installed Windows change the pagefile to reside on the small partition and create it equal to the size of your memory. Then there is enough space to defrag it (as even page defrag needs twice the space to enable a copy of the pagefile) and as long as you don’t use the small parition for anything else it never gets fragmented. This I’ve found stops that pause for 30 seconds with massive HDD activity on Windows OS’s. I’ve started to get pee’d off with my hibernation wake-up taking ages and I’m just about to create another small partition to try the same trick with my hibernate file!

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