[hydra-dev] * Fault Tolerance vs High availability

[Ed Guy]

Hydrates,

During the meeting a couple months ago,

there was considerable discussion about fault-tolerance.

In my book,  Fault tolerance implies that if there is a system failure
on a component that involves an active call, the call is migrated,
without significant
interruption, to another component.

is this really a requirement??? Most carrier grade systems merely
require high availability. i.e., if a
component fails, a call may drop, but the next call must go through. (
"fives-nines" or better of the time )
 
Fault tolerant architectures are very expensive and inefficient, but,
sometimes you cant afford any failure.


/ed