The R805 consumes 207 watts at rest (that is, running the operating system, but no virtual machines) and 411 watts under maximum load (running Dell's stress test software utilities). The R905 tips in at 331 watts at rest and 652 watts at full load, suggesting that performance (tiles per watt) is close to equal for both systems. The consumption numbers are good. The R805 barely consumes more power than a high-end workstation.
Head of the class
Dell's decision to provide virtualization-optimized servers is a smart move. Currently, it is the only server vendor to offer these systems. HP, by comparison, states that all its servers are optimized for virtualization, although this claim seems hard to accept in view of conflicting demands that might disfavor virtualization-friendly features. I suspect Dell's innovation will eventually require matching responses by both HP and IBM to cater to enterprise adoption of virtualization, especially in light of Microsoft's recently released hypervisor, which will further stimulate adoption.
The two machines are both very good solutions, the R805 being a journeyman and the R905 the greater professional. To my view, the R805 is a little limited and only SMB-class businesses will find its two-processor approach sufficient. Moreover, if a business wants local storage on its virtualization server, the two-disk ceiling will quickly prove limiting. Pricing and performance are good but not exceptional on this model.
The R905 is a far more complete solution. With double the number of processors, double the RAM capacity, and more than triple the disk space, it is a true enterprise or medium-sized business solution that provides plenty of room to grow. It also has the best posted performance for servers in its category. Given that, at retail, it's only US$5,600 more than the R805, it is easily the preferred solution and an excellent system.