RE: availability and resiliency

["Roeland M.J. Meyer" <rmeyer () MHSC com>]

It refers to the percent uptime of a host or site. 99% is two "9"'s
(2x9?) and 99.9% is three nines. Getting a single host to meet more than
three nines (99.9%) can be a challenge ( <8.76 hours outage, per year),
but can be more easily met with multiple hosts in a site. Four nines
(99.99% uptime, <0.88 hours annual downtime) is extremely difficult for
a single host, less difficult for internal data centers, and (given lots
of $$$) a bit easier for a internet site (using multiply redundant
hosts). Five nines (99.999%, <5.26 annual minutes down) is almost
impossible for a single affordable host to meet. This is where we enter
the world of High-Availability (H-A) systems. These are usually high
transaction flow critical systems and are found in large corps, telcos,
and reliable internet sites. At this time, only governments are willing
to part with the required cash to build systems meeting six nines
(99.9999%, <0.53 minutes annual downtime), or better (NASA, NORAD, US
Space Command, etc). Usually, this is done using multiple site
redundancy.
 
Hosts meeting three nines, or better, typically have redundant power
supplies and integrated UPS, bootable RAID for the OS, redundant NICs,
and SMP CPU configurations.

-----Original Message-----
From: Leo Nelson [mailto:lnelson () axient com]
Sent: Friday, September 29, 2000 10:08 AM
To: 'nop () alt net'; Andrew Bangs
Cc: nanog () merit edu
Subject: RE: availability and resiliency



Pardon my ignorance, but what the heck does a "9" refer too? Is it a
UPS, rack, floor space, circuit... 

Thanks in advance 
-leo 

-----Original Message----- 
From: Lionel Lauer [ mailto:longword () newsguy com] 
Sent: Friday, September 29, 2000 10:54 AM 
To: Andrew Bangs 
Cc: nanog () merit edu 
Subject: Re: availability and resiliency 



On Fri, 29 Sep 2000 17:39:04 +0100, Andrew Bangs <andrewb () demon net> 
wrote: 

> On Thu, Sep 28, 2000 at 02:39:40PM -0600, Irwin Lazar wrote: 
> > Hi all, 
> > Does anyone know if a template exists for what it takes to provide 5
9's of 
> > availability, 4 9's etc.for Internet data centers?  Specifically I'm
looking 
> > for something that would say "if you want 5 9's of availability,
here's what 
> > you need to do", and so on. 
>
> For 5 9s you need: 
>
> 1) Lots of money 
> 2) Lots of clue 
> 3) Lots of luck 
> 4) Lots of balls 
>
> You can do 4 9s with any 3 of the above. 

Too true. 

But you forgot to include 'halfway-clued management' - without that you 
haven't got a hope in hell of even getting three 9's. ;) 

-- 
   W          
 . | ,. w ,   "Some people are alive only because 
  \|/  \|/     it is illegal to kill them."    Perna condita delenda est

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