Hardware requirements for VPS is pretty interesting; in the sense of a problem to be solved. CPU performance has improved significantly year
after year, to the extend that 10 x 5-year old servers, which used to cost $5000 each, can be converted to 10 VPS, and placed into 1 physical server,
which cost $5000, and can perform well... if CPU is all that matters.
Unfortunately, the 5-year old server with a U160 10K SCSI, compared to the new server with 15K SCSI is not very far off in disk IOPs performance.
Disk IOPs is the bottleneck in many servers, rather than CPUs. In sizing a server for hosting multiple VPS, we need to put in as much RAM as
possible, to allow the OS to use the RAM for cache, and avoid reads where possible.
Next, choose storage with high random RW IOPs. eg. RAID 10, 15K drives. And possibly SSDs if the performance justifies the price. Intel quotes
very high 4KB IOPs for the X25-E and X25-M. Very tempting. Unfortunately, the details of tests done are not available with the spec sheets. Stating
"8GB span" and "up to" in the spec sheet is not all that reassuing. Performance is also known to vary significantly during benchmarking tests,
depending on how much of the SSDs is used, and length of test runs.
I have several pieces of the X25-M and X25-E, and will be testing the SSDs. If they produce at least 3 times more IOPs, sustained, compared to
15K drives, they are going into our next generation of VPS servers.