While fully compatible with its four-core Xeon predecessor, the new Xserve is new in some key ways that set markedly higher standards for performance and flexibility. Intel's Harpertown Xeon CPUs bring a cooler (meaning less hot) 45-nanometer manufacturing process to the mix, as well as a whopping 12MB of Level 2 cache per socket. The new Xserve's PCI-Express 2.0 bus welcomes the latest high-speed network and host bus adapters, but the expansion bus maintains compatibility with PCI-X cards that have been in the Xserve family since PowerPC.
Another throughput-boosting enhancement is the shift from 667MHz FBDIMM DDR2 RAM to 800MHz modules. Paired with Harpertown's per-socket L2 cache of 12MB, higher-memory bandwidth opens up the total system headroom needed to make worthwhile use of eight processor cores. Most commercial software is more throughput-bound than CPU-bound. On Intel architecture machines, RAM, bus, and cache are where you really feel the difference. The new Xserve delivers on all three.
Apple has added an onboard AMD/ATI 3-D GPU (graphics processing unit) with 64MB of video RAM. This allows the frequent use of Xserve's console, including Apple's demanding Aqua GUI, without inflicting the drag on the CPUs and main memory that Intel's integrated graphics does. For creative and scientific applications where the onboard GPU isn't enough, Xserve can be purchased with a PCI-Express graphics adapter. Though a server acting as a workstation is not a corporate usage scenario, where batched server workloads are the norm, there's no reason to let Xserve's console lay dormant between runs. Xserve's standard SuperDrive dual-layer DVD burner reflects that Xserve is flexible enough to be harnessed by a user.
In a small-business setting, Xserve's improved ability to handle interactive tasks can be a real boon. While Xserve is too loud to make a good office mate, placing it in a noise-isolated chassis (like GizMac's XRackPro) or using affordable video and USB extension cables may obviate the need for a desktop. OS X Leopard Server runs the same applications as the OS X Leopard client operating system shipped with Mac notebooks and the Mac Pro desktop/workstation. Unorthodox? Certainly, but giving a server whose utilization floats around 30 per cent the pleasure of serving a user seems fit for the present economy. Apple further enhanced Xserve's local usability by placing a USB port on the front panel.
Server-based storage is one of Xserve's strong points, and Apple has taken it to an extreme. As before, Xserve has three bays for removable drives, and each bay accommodates not only the Serial ATA drives common to entry PC servers, but also SAS (serial attached SCSI) drives that spin at up to 15,000 rpm. You can configure your Xserve with any mix of SATA and SAS drives, setting your own balance of speed and capacity. On the subject of capacity, new 1TB Apple Drive Modules, which are compatible with the preceding Xeon Xserve as well, bring the total server-local storage capacity to 3TB.
At around the same time that Apple shipped the new Harpertown server, it delivered a hardware RAID card that is installable in any Xeon Xserve. This US$999 option is invisible once installed; it replaces the backplane into which the SATA and SAS drive bays plug, and therefore does not consume a precious expansion slot.
Hardware RAID changes the character of Xserve, carrying it into an entirely new class of server. The RAID add-in is the real deal, with battery-backed write cache, transparent and autonomous building and rebuilding of parity and mirrored volumes, and boot capability even when a drive in a parity set fails.
I consider the RAID option non-optional for commercial use. Its only downside in my testing was frequent complaining to the console whenever the battery's charge wasn't sufficient to hold data for 72 hours without power. It says something about the RAID controller that it considers 72 hours a low-water mark for cache retention after the plug is pulled, but I can do without the notices.