Xah Lee's Unixism

Steve O'Hara-Smith steveo at eircom.net
Thu Sep 9 23:26:53 CEST 2004


On Thu, 09 Sep 2004 17:21:15 GMT
Nick Landsberg <SPAMhukolauTRAP at SPAMworldnetTRAP.att.net> wrote:

> jmfbahciv at aol.com wrote:
> 
> > In article <20040908192913.67c07e7d.steveo at eircom.net>,
> >    Steve O'Hara-Smith <steveo at eircom.net> wrote:
> > 
> >>	The Yahoo! server farm ran to very long uptimes last time I had
> >>any details. The reason being that they commission a machine, add it to
> >>the farm and leave it running until it is replaced two or three years
> >>later.
> > 
> > Sure.  But regular users of such computing services never get an
> > uptime report.  Hell, they have no idea how many systems their
> > own webbit has used, let alone all the code that was executed
> > to paint that pretty picture on their TTY screen.
> > 
> > I bet, if we start asking, we might even get some bizarre
> > definitions of uptime.
> 
> Well, there are lies, damn lies and statistics, don't
> you know? :)
> 
> I have absolutely no idea of the size of Yahoo's "server
> farm," but let's assume that it's roughly 100 servers
> to make the arithmetic easier.  Let's further assume
> that the MTBF (Mean Time Between Failure) is roughly
> 2000 hours (about 3 months, or about 90 days).
> 
> Given these numbers (which are not real, I remind you,
> just made up), it is likely that on any given day
> one of those servers suffers some kind of failure.
> However, one can argue, quite legitimately, that
> the service which Yahoo! provides is still "up and
> running."  1% of the users may not be able to access
> their mail for a few hours, for example, but the Yahoo! is
> still running.

	Erm in this case the farm is a search engine service, if one of
the machines goes down then the searching gets a bit slower for everyone.
At any rate the report from inside Yahoo! was that they considered it
normal for a machine to run uninterrupted for a couple of years and
then get replaced.

> > I do know that the defintion of CPU runtime is disappearing.
> > 
> 
> Not everywhere, Steve.  There are still shops

	That's /BAH you're responding to there :)

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