Apple's Nehalem Xserve serves the need for speed
Sleek, new Mac OS X rack server sets a far higher bar for performance and power efficiencyFollow @infoworld
That's no typo, and you should set aside your inclination to write off STREAM as a predictor of real-world server performance. In SPECjbb2005 (Java business benchmark) tests, the original eight-core Xserve scored 36,688 operations per second, while Nehalem Xserve managed a score of 83,926.
With only 8GB of RAM to Nehalem Xserve's 24GB, the older server was underconfigured by modern standards, a fact that may have contributed to its poor showing despite the fact that the machine did not resort to paging processes out of RAM during testing. Poor scalability under parallel memory-intensive loads was a characteristic of Intel x86 pre-Nehalem, symptomatic of a bus architecture that imposed a heavy penalty on memory access. That penalty is gone.
The smooth scalability of Nehalem Xserve under rising parallel load in the SPECjbb2005 tests not only highlights the Nehalem architecture's improvements, but also Mac OS X Leopard Server's exploitation of the architecture. The kernel's deft assignment of tasks to processor cores and thread units, and its mapping of physical memory to leverage NUMA (non-uniform memory architecture), keeps Nehalem Xserve's six memory channels working together. It took Microsoft several years to fix Windows Server to make appropriate use of AMD64 NUMA, the model Intel adapted for Nehalem. If early benchmarks are any indication, Apple seems to have gotten NUMA right on its first try.
Ecofriendly -- to a point
The 2.26GHz Nehalem Xserve is probably the greenest server this side of UltraSPARC T2, and for many uses, it will outperform the eight-core, 3GHz model it replaces. Xserve meets Apple's exacting standards for environmentally responsible manufacturing -- it's so non-toxic that it's practically edible -- but in its maxed-out 2.93GHz, eight-core incarnation, Nehalem Xserve is more about high speed than low power. Mac OS X Leopard Server lacks the equivalent of Windows Server's energy profiles. There's no way to make the server less than it is for the sake of enhancing savings and quiet at times of low compute demand.
The new Xserve's power draw at idle is higher than that of the previous Xserve. That said, Xserve makes a greater effort than most rack servers to run as quietly as its workload permits. The fan array can get loud, but Xserve never emits the piercing high-frequency din that high-end 1U rack boxes can broadcast. Nehalem Xserve's noise is very effectively muffled by my GizMac XRackPro.
One power-saving option holds great appeal for shops that make heavy use of networked storage. Apple now sells a 128GB solid-state (flash) boot drive for Xserve. This can greatly reduce power consumption, heat, and noise, and with no seek or rotational latency, the system loads the kernel and apps lightning fast. This comes at the expense of write speed, though. With its plentiful cache, further abetted by the cache on the server's optional hardware RAID controller (highly recommended), a single 1TB Western Digital SATA drive was two to three times faster in write performance than the SSD. Look to the solid-state drive option to simplify and slim your Xserve, not to speed it up.
The lack of power controls is a shame because no x86 server is better equipped to make smart decisions about power than Xserve. The temperature, voltage, and current draw of most major components are tracked continuously and reported to Xserve's independent system management controller, which Apple calls the "LOM," for "lights-out management." LOM data is readable with Apple's Server Monitor GUI or the ipmitool command-line utility. The LOM shares one of Xserve's two gigabit Ethernet ports, using its own IP address and security credentials.
Apple's Server Monitor GUI provides power control and boot image selection when Xserve is shut down.