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Eight hardware threads in a four-processor system -- that's the innovation behind the Sun Fire V490, one of the first two models to use the company's new dual-core UltraSparc IV chip. (The other is the eight-processor Sun Fire V890, released at the same time.)

The new processors give the V490 a significant boost over its V480 predecessor, but the server is less than state-of-the-art in I/O and fault-tolerant features. The V490 is appealing for applications that require a lot of processing power, such as data mining, scientific computing, or other CPU-bound tasks.

Two cores, no waiting
Architecturally, the V490 is a straightforward upgrade of the Sun Fire V480, which used four UltraSparc III processors. Both servers are 5U high and contain two internal disk drives, six PCI slots, an onboard management processor, and a maximum 32GB of memory plus redundant power and cooling.

These internal workings make the V490 best suited to computing in an environment with external storage, such as in an n-tiered architecture, a load-balanced cluster, or other transaction-processing environment, as well for server-consolidation applications that would run multiple simultaneous threads.

The biggest enhancement in the V490 is the dual-core UltraSparc IV processor, which runs at the same speed, 1.05GHz, as the V480's UltraSparc III. The newer processor design lets the V490 handle two threads per chip, which works out to eight hardware threads in the entire server versus the four threads in the V480 server. So you almost get an eight-processor server with the form factor and power/cooling profile of a four-way server.

Why almost? Because multi-core processors represent a trade-off: Shared components mean that you don't get exactly twice the performance as you would using two discrete microprocessor components but they do present a huge reduction in space, power consumption, and cost. It's a good trade-off, and one that would work fine in nearly all circumstances, but a trade-off nonetheless.

Here's the setup: the implementation in the UltraSparc IV shares common components between the two cores within each physical chip, including memory and bus lines. Each core, however, has its own Level 1 and Level 2 cache, so they can run independently; there's no compromise or contention for the precious cache.

The shared bus and memory lines aren't a problem when the server is running applications in which there would be external wait time, such as waiting for disk or network I/O in a transaction processing context. With those applications, the V490 performs like an eight-processor server -- perhaps even faster. Inter-thread communication between the two cores of a single processor should be speedier than communication between two separate physical processors.

However, in applications where there's little I/O wait time and the system is performing many memory-intensive operations, the shared memory and bus lines may retard overall system performance. In those situations, the V490 would show little or no improvement over a four-processor system.

This is a case, however, where the big picture matters more. Overall, the benefits of dual-core processors -- including cost, space, and power consumption -- far outweigh any minor situations where they might not perform as well as dual physical processors. In that regard, the V490 is a definite improvement over any comparable single-core system, such as the V480.

I/O hits a wall
The Sun Fire V490 we tested was equipped with its maximum four 1.06GHz processors, 16GB of memory, and a single 73GB 1Gbps FC (Fibre Channel) drive. It was preloaded with Solaris 9 and Sun's JES (Java Enterprise System), which included the J2EE application server and other software.

Because raw performance testing was not the focus of this review, the applications weren't particularly tuned, but a simple Web application loaded onto JES ran smoothly and reliably for the three-week duration of our system tests.

One disappointment with the Sun Fire V490 is that it shares the same I/O configuration as its 2 1/2-year-old predecessor. Both servers have dual 1Gbps FC drive bays, which limits most production deployments to using external SAN or NAS storage systems, because the dual drives would likely be required for a mirrored boot configuration. The V490's dual-core sibling, the eight-processor Sun Fire V890 server, uses a faster 1.2GHz UltraSparc IV processor and offers 12 drive bays in its 17U form factor.

The V490 has the same 9.6GB/sec backplane as its predecessor, as well as the same six PCI slots, two of which are 64-bit 66MHz and four are 64-bit 33MHz. That I/O subsystem simply isn't enough to keep up with the blistering I/O that an eight-thread system should be able to perform in a modern environment.

We'd expect a new server in this class to have at least two 64-bit 133MHz PCI-X slots, and preferably four. Optimally, it should have the capacity to handle the new PCI-X technology via an I/O board swap. The V490 falls short of these expectations. (Surprisingly, the new V890 has a similarly limited six-slot PCI I/O subsystem, with two 64-bit 66MHz and seven 64-bit 33MHz slots.)

Weighing the benefits
On the fault-tolerance side, the system offers only the basics, with hot-swap power supplies and cooling. Keep your screwdriver handy if you want to pop the top to get to a fan or slot: The engineers at Sun clearly don't buy into the no-tools-required design philosophy popular at Dell, HP, and IBM. You won't find mirrored or hot-spare memory, either -- another spot where the V490 is sadly behind the state of the art.

Despite these weaknesses, the Sun Fire V490 represents a step forward in RISC-based server technology. The price of the tested system is about 37 per cent higher than a comparably equipped Sun Fire V480, an increase directly attributable to the new dual-core processors.

For CPU-bound applications, that's a bargain, and the Sun Fire V490 is very appealing. For I/O-bound applications, however, you're better off with buying the older server -- or getting a Sun Fire V490 only populated with two processors.