Critique?

[dsr at tao.merseine.nu (Dan Ritter)]

On Wed, Feb 28, 2007 at 04:39:27PM -0500, markw at mohawksoft.com wrote:
> > On Wed, Feb 28, 2007 at 02:41:29PM -0500, markw at mohawksoft.com wrote:
> >>
> >> The Myth of Five Nines
> >> http://www.mohawksoft.org/?q=node/38
> >
> > Multiple geographically disparate (and network-topologically,
> > and power-grid) sites are indeed a requirement. They are not
> > rare, however, and not necessarily budget-busting.
> 
> Come to think of it, maybe not, if you can lease in some managed site, but
> they aren't that cheap.

It All Depends, of course.

Let's suppose that your company derives revenue from online services. That
is, it's a profit center, not a cost center. How much more revenue will
you generate from being nominally up 24x7 versus having a five hour
maintenance window one day a week in the pre-dawn hours? And how much
revenue do you lose when a customer expects you to be up at an odd time
but you aren't?

On the other hand, there are internal uses which are cost centers. Pretend
that you run IT for a regional chain of retailers. Inventory and sales
figures need to be tracked, but how much is it worth to be able to have
those in real-time versus end-of-day versus end-of-week?

Size matters. A 50-person company thinks differently about 3
more hires for 24x7 ops than a 500-person company.

These calculations will tell you how much it's worth spending on increased
uptime. Some businesses need it, some won't. Some commitments to 24x7
service will make others cheaper, since you may have already sunk the
cost of building out a second datacenter, or a 24x7 operations crew.

And there are different levels of costs. If your net presence is
three webservers and a database, even a complete doubling of
hardware in a far off location may not be too expensive. If it
is, perhaps a virtual host on the other coast of the US will serve
your emergency needs by simply showing some static pages when you
have a problem with your main site.

> Oh, no doubt, I wasn't trying to slam Microsoft, (Though it is something I
> do enjoy) I was more pointing out that even the best funded sites have
> unexpected issues. The point is that you can't plan for every eventuality.
> Sooner or later you will have a failure of some kind.

Sure, and that's why we talk about nines of reliability: to give
an estimate of what we expect, or a measurement of how well
we've done.

-dsr-

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