Rajagopal Swaminathan wrote:
> On 3/24/11, Akemi Yagi <amyagi@xxxxxxxxx> wrote:
>> I should note, however, that they are not for production use.
<snip>
> </rant>
<snip>
> I am sure you have heard of Hanuman from Ramayana the best grammarian
> known?
>
Huh - it's been more than half a lifetime since I read a translation of
the Ramayana, or maybe it was the translation, but I don't remember
Hanuman as grammarian. <g>
> </rant>
>
> Having said that, I have this troubling thought for last decade: What
> exactly is high availability: is it 24/7 power on time? or is ti "when
> needed". Please not it am not talking about the maybe arrogant "on
> demand" attitude of a human.
Ok, h/a is not "fault tolerance", which is for 99.+% uptime (and you *pay*
a lot for additional decimals there). What it is for is well over 90%
uptime, though where I've worked, including supporting the City of Chicago
911 system (emergency system, that is), it was expected to be over 99%
uptime. h/a, as you should be familiar from your experience, two or more
servers share an asserted IP address, and if one server goes down, another
will see within whatever's configured - 30 seconds, maybe - the other
server then asserts the IP address, and offers all of the services
expected. They should also be sharing redundant storage, so that the only
thing that should be lost are transactions that were just started when the
first server went down; those that were partly transacted should be rolled
back to a known state when the second server asserts the IP.
>
> I never understood the term "Hig Availability" : does it mean
> available as in "soliciting" ?
Nope - it has real meaning.
>
> What exactly those lusers want? and what exactly we self declared high
> tech droids / engineers seek?
>
> What exactly is "production" use? (I know DEV, UAT, blah, bla, tla
> etc been there done that and I don't have the T shirt - nobody gave me
> one)
All services expected from a server at a given IP should be available up
to or over 99% of the time, with no lost transactions, or transactions in
an undefined state - that's h/a and production.
mark
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