At 7:14 PM +0000 6/12/03, Aaron Ajello wrote:
>every time I have seen a percentage uptime quoted, it has NOT included
>regularly scheduled maintenance time.
>
>a year has 8760 hours. 99.999% of which is 8759.9 hours, which leaves .1
>hours (6 minutes) for downtime. that would be tough.
>
Organizations that seriously want to get this kind of uptime have to
build in extra equipment so there's never a need to take services
down for maintenance. There's a telephony motto "once up always up."
A typical critical component in telephony, brokerage, etc., is
triple-redundant.
1 active component
1 hot standby
1 standby or in maintenance.
Depending on the system design, you may loadshare among the working
resources. The key design decision is whether your users can accept
degraded performance if not all resources are usable.
In operational scenarios, you might, for example, take a standby
router down and upgrade the IOS. You'd then designate it as the
standby, and take the previous standby down and upgrade it. You'd
then switch from the active to the standby and upgrade the active.
Now, whether or not your executives still want five nines after
seeing the cost is another question. Not infrequently, the way to
get this is not to do it all yourself, but put resources at colo
centers that can amortize the highly redundant equipment over many
customers.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=70604&t=70595
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