There have been some questions about H-Sphere's capacities in a single server implementation, so I am sharing what I know here:
Psoft, as a responsible software developer, must err on the side of caution in pointing out limitations of single server implementation. The fact is, H-Sphere does run completely fine on one machine and the only limitations we are aware of are the following:
1) Postgres instance must be used by H-sphere, and you cannot have second instance running on the same machine for your customers.
2) Capacity is determined by the activity of clients - could be 5000 "dead" accounts or 100 average ones or 5 very active ones.
It is also makes a big difference if the servers are designed for hosting.
There are architecture elements that you would never miss in a desktop computer that would seriously slow you down in a hosting environment. Hosting servers are best with SCSI drives because SCSI read a large number of small files (like on websites) 20 times faster than IDE which has a reading arm that must skip around to each sector of the drive to pick up each individual file. That's also why IDE will fail faster in a hosting environment.
Also the RAM is much faster if it is SDRAM, which is registered to work with buffers (and the computer it is in can accordingly take advantage of buffers).
Machines of this type are more expensive, but the capacity, performance and reliability are a big savings in the end. If you wonder what such a box looks like, there is a picture on our site at www.smartfunction.net/ibm
Despite the single server capacity, multiple H-Sphere machine installations are more efficient than single server implementations. That is:
capacity of a 2 server H-sphere implementation > capacity of 2 single server implementations
By the way, capacity of a 4 server implementation > capacity of 2 double server installations.
After 4 machines, the additional efficiencies of scale continue.
We have clients with 20 servers - scales perfectly, and works much better than it would be with 5 clusters of 4 servers each.
There are some creative things you can do as far as putting dual processors with the elements doing the heavy lifting, and save money not doing it with the others. That's when having the computer architecture designed for hosting really helps you, because you HAVE the slots to put in multiple processors, extra drives, and boatloads of SDRAM.
I really hope this helps settle some of the questions about use of this very powerful and feature-rich software.