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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: availability and resiliency
Title: RE: availability and resiliency 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.
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