In their six cores, the Opterons offer exactly six threads of execution. Today's Nehalem Xeon processors from Intel come with four cores, each of which can run two threads of execution simultaneously, using Hyper-Threading. Consequently, a quad-core Intel Xeon offers more threads per chip. However, two Intel threads share a single 256KB L2 cache, while the cores on the AMD Opteron are given a full 512KB of L2 cache each. How much of a difference this cache makes depends entirely on the workload. Light workloads that do not require large amounts of data in RAM to complete transactions will work well on Nehalem servers with Hyper-Threading enabled. Database applications and enterprise workloads will prefer the greater cache of AMD Opterons. (The Nehalem chip's Hyper-Threading can be disabled to reduce -- but not eliminate -- the cache limitations; however, this step limits the chip to a total of four threads.)
With a total of 12 threads on the R805 and 24 on the R905, Dell's servers provide plenty of processing power. Only a severely overloaded server is likely to exhaust the processing capabilities of these chips. And it would be more likely that such a server would run into RAM constraints before maxing out these CPUs.
A final requirement of virtualization servers is plenty of bandwidth. These systems are not intended to provide the primary storage for the VMs, nor for their workload. As a result, the servers tend not to support large numbers of high-capacity disks on-system. Rather, they depend on accessing both VMs and data via the network. Because of this design, which is increasingly common in servers of all types, virtualization servers typically have numerous large pipes. The R805 and R905 both have four slots stocked with 1GbE cards that support TCP/IP offloading (TOE). Two of the four slots can hold 10GbE network adapters.
One obvious requirement of all virtualization servers is the ability to boot an operating system that runs a hypervisor. Both Dell systems enable users to boot at least two different operating systems. There is the OS on the hard drives, which in the case of this review was Microsoft Windows Server 2008 running the Hyper V hypervisor. And there is a second optical drive that plugs into the internal USB port. At boot time, it's possible to set the machine to boot from this drive rather than the hard drives. Consequently, with both systems, you can run different hypervisors without having to configure the software or the hardware. For many sites, this is not an important advantage, as most IT organizations choose one hypervisor as the standard and build their infrastructure around that choice. However, sites with multiple hypervisors in use will be able to move these servers back and forth between hardware pools without having to reconfigure them.
Test results and report cards
There are three standout results in the benchmarks of these systems when compared with last year's models. All have improved in conspicuous ways, especially with respect to performance and power consumption. The R805 is also significantly more affordable than last year's model.
Dell virtualization servers by the features
|Dell PowerEdge R805||Dell PowerEdge R905|
|# of CPUs/sockets||2/2||4/4|
|Type of CPU (as tested)||AMD Opteron 2435 2.6GHz||AMD Opteron 8435 2.6GHz|
|Installed RAM/max RAM||16GB/128GB||32GB/256GB|
|RAM type/speed||DDR2 ECC, 667MHz||DDR2 ECC, 667MHz|
|# of RAM sockets used/total||8/16 DIMM slots||16/32 DIMM slots|
|# of PCIe slots||3 x x8, 1 x x4||2 x x8, 5 x x4|
|USB ports front/back/internal||2/2/1||2/2/1|
|HDD installed/slots (2.5-inch)||2 x 73GB / 2||2 x 73GB / 4|
|Network ports||4 x 1GbE w/ TOE||4 x 1GbE w/ TOE|
|Power supply options||2 x 700W||2 x 1100W|
|Tool-less case design?||Yes||Yes|
|Chassis type||2U rack||4U rack|
|Price as tested||$7,643||$18,906|
|Warranty||3 years, next business day||3 years, next business day|
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