This is somewhat off the topic of your questions, but...
The AOLserver clustering support in OpenACS seems like a useful
addition for flexibility, but I'm not sure how relevent it really is
for a current site with any sort of reasonable hardware budget.
Supermicro now sells 4-socket Opteron servers at no price premium over
1 and 2 socket boxes; they're priced essentially linearly with the
number of sockets. That means you can easily buy an either
1u or
2u
box with 4 sockets, 48 cores, and 256 GB of RAM for $15k or so. (You
can go up to 512 GB RAM on that same 4-socket motherboard, it just
gets pricier.) How many OpenACS sites need more than 48 cores and 256
to 512 GB of RAM for their web servers? My guess is that's plenty
even for big sites like WU-Wien. Spend a little more on disks and
possibly a good hardware RAID controller, and you could also use that
same 2u box for your RDBMS.
For more disk-intensive RDBMS loads, particularly analytics rather
than the more OLTP-like loads typical of most OpenACS sites, I'd like
to try some of Scalable Informatics'
JackRabbit
and/or DeltaV boxes. They seem to give massive streaming IO bandwith,
and if one 48 disk box isn't enough, they also offer them configured
as a storage clusters, optionally with a high-end Infiniband interconnect.
For the high-end storage cluster route, I'm not sure if any of the
current cluster file systems are suitable for running an RDBMS, but if
not, it'd probably work reasonably well to have your single RDBMS box
use each of those 48-disk boxes as a giant "local" RAID-10 array.
You'd want to make sure the PCI-E bus(es) on your RDBMS box can handle
the bandwith, though. At some point that single RDBMS box will top
out, and to get even more CPU and/or disk IO, you'd need to either
look at more specialized (and pricey) giant SMP/ccNUMA boxes, or real
shared-nothing clustered databases - Teradata or their newer cheaper
competitors (some of which are PostgreSQL based).
