This is a good choice for compute-intensive applications, but the System x3455's restricted storage and availability options limit its use when it comes to general hosting duties.

IBM System_x3455Like both Dell and HP, IBM sells a variety of industry-standard servers based on Intel dual-core, and now quad-core processors. However, IBM was also one of the first server vendors to use AMD silicon, and the model we looked at, from its xSeries family, is based on the latest dual-core Opteron chips introduced in 2006. There are several different AMD models in the xSeries line-up: the System x3455 is a 1U rack-mount server targeted primarily at customers looking to run compute-intensive scientific, technical and financial modelling applications. As such, it can be fitted with two dual-core Opteron processors but is somewhat restricted when it comes to storage and redundancy options.

On the plus side, the two processor sockets are capable of accommodating a variety of chips from the 64-bit Opteron 2000 family. These processors are designed specifically for two-way server deployment.

Clock speeds vary from 1.8GHz on the Opteron 2210 through to 2.8GHz on the 2220; our review system came with a pair of 2.6GHz 2218 chips fitted. However, as with the Intel processors, some care and advice is needed here as unused power can be expensive -- as can be upgrading to faster processors should the initial configuration prove inadequate.

Note, too, that slower chips are more energy efficient, enabling the x3455 to get by on just 95W compared to around 110W with the fastest processors installed.

Other than these differences, the processor specification is much the same, with 2MB of L2 cache per socket (1MB per core), support for DDR2 memory and built-in hardware virtualisation features (AMD-V) -- useful when running applications such as VMWare, Microsoft Virtual Server and Xen Server software.

Naturally the processors also feature support for AMD's Direct Connect architecture, which does away with the concept of a frontside bus. Instead, the memory and data I/O are all managed directly by the CPUs, with on-die controllers able to communicate at processor speeds. This approach also provides much more linear scaling as processors and cores are added, with dedicated HyperTransport links for inter-processor and external I/O communications.

What this all means in actual performance terms will depend on the overall configuration. However, in independent benchmarks dual-core AMD Opterons have generally been found to outpace Intel's Xeon equivalents. Moreover, it has no effect whatsoever on compatibility, with the x3455 and other AMD-based servers certified for and able to run the same range of Windows, Linux and other industry-standard server software. Depending on the reseller, you can also have an operating system and application software preinstalled.

On the downside, quad-core Opterons are not yet available (they are planned for release later in 2007). However, the new processors will use the same socket as the existing dual-core designs, so the x3455 and other AMD Socket F-based servers will be upgradeable in much the same fashion as those designed around the latest dual-core Intel Xeon chips.

Our test server had a basic 2GB of memory fitted, while the maximum capacity on the x3455 is 48GB using 667MHz DDR2 SDRAM with six DIMMs per processor. This is part of what IBM calls its Xcelerated Memory Technology, which it claims enhances the level of performance possible over comparable Intel-based platforms. Note, however, that the memory is interleaved, so DIMMs have to be added in pairs with ECC and optional Chipkill support so that the server can continue working should a DIMM become defective.

Unfortunately it's not all good news, with the biggest limiting factor on the x3455 the provision of just two 3.5-inch internal hard disk bays. That limits storage capacity to 1TB using SATA-150 drives or 600MB with SAS, which is reasonable enough. However, there's no support for hot-swapping and the fact that there are just two spindles limits the level of redundancy that can be provided. Indeed, with just two spindles the built-in RAID controller is limited to fixed mirroring/duplexing -- although plug-in adaptors can, of course, be used to connect the IBM server to larger, more flexible, external storage arrays and SAN set-ups.

Two Gigabit Ethernet interfaces are provided, but there's no TCP offload support and you only get two 64-bit PCI-Express expansion slots. One of these can accommodate x16 adaptors while the other is an x8 slot that can also to take so-called HTx cards designed to interface with the I/O subsystem using the AMD DirectConnect architecture. An InfiniBand card is one adaptor that can take advantage of this format.



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