> "Clark, Joel" wrote:
> > Yeah, I was really just curious if the proposed system was at a system level
> > or a network level. Having two physical machines share (at the system i/o
> > level) a storage unit is something I have never heard of. Does such a beast
> > exist?
> Yeah, they exist, though why they exist is beyond me. Maybe because
> windows systems crash all the time. It doesn't make much sense to me,
> after all it would seem that hard drive failure happens more often that
> the system crashing for no reason.
they exist for a variety of reasons.
most importantly however, a hardware cluster was one of the first technologies on the scene (and still a very important one today)
that offered redundancy and load balancing. remember, a system often crashes, not because of hardware failure, or o/s failure
(excluding windows of course), but rather application software failure. the need for hardware redundancy solved that problem as
well as the remote problems of other non-disk related failures. just because a failure doesn't happen often doesn't mean it is
acceptable. how do you think the banks, or airline traffic controlers would feel about that?
Digital basically pioneered the entire front, as their hardware and o/s were most often used in critical systems demanding 100%
uptime. since then the technology has moved around a bit. (arguably, one of compaq's main interest's in digital was clustering
technology). most unix systems have some kind of clustering available. today, most outfits go the replication route. however, for
truly mission critical systems, replication is still not an acceptable option, for the simple reason of too much latency and lossy
performance. even with the giant leaps forward in network bandwidth, replication technology still has a long way to go before it
will be considered for the most critical of applications.
one of my major issues with postgresql is its contractidory stance on performance:
how can you be a frontier database with a (at best) sloppy high availability/load-balancing strategy?
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