O's modular software architecture also promises greater drive stability and more flexibility and competition i
n the server arena.
But exactly what the performance improvement is, or how flexible I
2
O will be in the real world, remains to be seen. At press time, Microsoft, Novell, and SCO were preparing to release either new or updated OSes with I
2
O support.
One benefit of I
2
O is the ability to scale servers. "Servers that do not have intelligent adapters spend a tremendous amount of CPU power managing the I/O in the system," says Harry Mason, director of host marketing at
Symbios
, which is developing numerous I
2
O products. "Often a user finds that he or she has adequate performance in a server [in its original configuration] but finds that the system bogs down when additional host adapters or more LAN cards are added."
Mason estimates that with traditional device drivers and nonintelligent adapters, you could expect to see 8000 or more I/Os per second in today's Pentium Pro-class machine. At those levels, the machine
might use close to 90 percent of the available CPU performance.
But with I
2
O and other intelligent approaches, a server might only use 40 percent of its CPU power for 8000 I/Os, and adding more storage-adapter cards could allow the system to scale to well beyond 20,000 I/Os before saturating the CPU. "This ability to grow the server to serve a wider range of departmental or enterprise needs -- and to do this in the environment of industry-supported standards -- is the real value that I
2
O provides to the end user," says Mason.
However, the concept of off-loading I/O tasks from the main CPU is not a new one. Supercomputers, mainframes, and other big-iron systems have done it for years. "I
2
O is not doing anything more than intelligent peripherals have been doing for some time," says Keith McAuliffe, vice president of engineering in Compaq's server-product division. "I
2
O does not make an equivalent [non-I
2
O] implementation go faster." What it doe
s do, according to McAuliffe, is establish an infrastructure that will permit hardware and software vendors to spend more time innovating and less time rewriting drivers.
Currently, in a non-I
2
O scenario, a hardware vendor has to write, integrate, test, and distribute a device driver for each OS and OS revision, each new controller board, and sometimes revisions of the controller. I
2
O's split-driver model can potentially eliminate all that busywork. With I
2
O, an OS vendor, such as I
2
O SIG member Microsoft, Novell, or SCO, writes an OS-specific module (OSM) for each class of device supported.
Then, companies making devices such as SCSI adapters, hard drives, and network interface cards (NICs) write one driver that works with any I
2
O-compliant OS that supports that class of device. "We would rather see innovation in other areas than have to use programmers' time to write and rewrite drivers for different OSes," says Tamar Newberger, director of
product management for UnixWare 7 at SCO.
Proponents say that I
2
O, by freeing vendors from the chore of writing and rewriting their drivers, could result in a more horizontal PC industry, where every layer has competition. Vendors would be able to concentrate on writing the best driver or the best RAID software.
The latter is exactly what Mylex hopes to do with the I
2
O RAID software it plans to release in the first quarter of this year. "Thanks to the modularity of I
2
O, our RAID software doesn't have to be intertwined with the SCSI chip," says Doug Fields, senior product-marketing manager for Mylex. "The software does not have to know the details of the hardware, so you can use it with a variety of SCSI chips." And, by taking advantage of the i960, Mylex's RAID software can deliver better performance than a software-only solution.
Vendors caution that I
2
O will not eliminate the need to write native device drivers, as I
2
O is not suppor
ted in Win 95, nor will it be supported in Win 98. In addition, due to the enterprise nature of I
2
O, software programs will require extensive testing before they are released, which could slow products' commercial arrival.
Meanwhile, I
2
O members are discussing adding even more features to future versions of I
2
O that will make it more robust. These features include support for peer-to-peer (where a NIC gets a file from a Web server's hard drive with minimal interruption to the CPU), Fibre Channel, clustering, ATM, WANs, and the hot replacement of peripherals.
photo_link (19 Kbytes)
The new Symbios I2O adapter supports Fibre Channel with faster 64-bit PCI.
I
2
O Getting Ready to Go
