There are many aspects to this.
* first of all, we applied for national hardware
grant and it looks as if our impressive numbers
and some vision helped us to get it. However, the grant
was purely a server-hardware grant and we are obliged
to spend the money for this purpose.
* Secondly, we got a very good deal on the machine,
much better than i expected (i can't talk about
prices here). There would have been
a significant price jump between the 2.7 GHz and 3 GHz
processors. Another, much more significant
price jump would have been heading towards itanium
machines. We got the machine without OS, put FC2
on it without any problems and that was it.
Concering just one big iron: there are a couple of
aspects:
- in our current setup (up to last week),
the biggest bottleneck
was the "dynamic" aolserver, followed by the
database server (with earlier versions of
postgres, it was the other way around).
so, using two n-way machines helps us
immediately without restructuring the
apps, thinking aboutflushing distributed
caches, etc. With this setup we are simply
on the safe side.
- Many of the dynamic requests depend on the
content repository and therefore the file
system. I did not make tests, but i would
not be surprised to run into problems when
different machines hammer around in the
same file-system (e.g. shared via NFS).
We are frequently thinking about further
distribution and more redundant backend
servers (managed by pound), we will go for it
when necessary.
- the two 8-way machines can be combined
into one 16-way SMP machine. So we have the
option to switch to one big database machine
in the future.
Alltogether, we are not only worrying about
performance, but also about reliability, robustness
and maintainability. The new machines can be maintained
over the web (rebooted etc), they are highly redundant
(they can have hot swap memory, but we did not go
for that), and they are nicely engineered.
Our system is seen as central infrastructure of a large and
important university. As it is with infrastructures
and utilities, people expect it to work 7x24 (but
we have no personnel for ensuring that). While many
(most?) learning management systems provide mostly print
materials (slides, handouts) in electronic form,
we have mostly interactive materials, providing immediate
feedback. So, the students really prepare for their
exams over the system, they rely on it. If our system
would work unrelyably, many people would be immediately
upset. If this would happen at a bad moment, we will most
likely make it to the newspapers. So, spending more money
in robustness seems worthwhile.
-gustaf
