Dell Poweredge 2950,
~Two Dual-Core Intel Xeon 5150 processor's at 2.66GHz 8gb,
~Windows Server 2008 R2 Datacenter, HyperV installed,
~32GB (8 DIMM slots): 4GB Fully Buffered Dimms (FBD) 533/667MHz
Error Checking and Correction (ECC) and Single Device Data Correction (SDDC),
~4.5TB HDD : 6 x 750GB SATA HDD (7.2K rpm) with 6 SATA/SAS Interposer boards,
~It also has the integrated PERC 5/i: SAS 3.0 Gb/s RAID controller with 256MB battery-backup cache,
~Redundant 750w power supplies,
I have the Host on a RAID 0 (2-750GB HDD's), and the other four on RAID 10. This gives me 3TB of storage to work with on the client side of things. I was hoping this girl could handle 25 to 35 VM's, but then I come back down to earth and hope for 15 to 20 client VM's. Hopefully I have given you guys enough information to help me clarify how many VPS clients this server might be able to carry.
15 to 20 is probably realistic, but 30-40 could be possible if you have very low disk I/O requirements for each machine. I would guess that your environment will first encounter a storage I/O bottleneck followed by insufficient RAM (2008 R2 can't over commit RAM) and finally a CPU bottleneck. But depending on the actual workload of each VM, you may hit those bottlenecks in a different order.
15 to 20 I would also say, and that number is smaller depending on the services/client OS. If your going to be virtualizing an Exchange server for example, I would say 2 per box would be your limit. If your going to virtualizing desktops, then 15-20 for moderate usage, 30 or so with light usage per server. The biggest issue you have is the amount of RAM per box, followed by the CPU power. I know for our virtualized environment, we host about 24GB of RAM for 10 medium-load servers, and 48GB to host between 50 and 75 end user desktops.