PALO ALTO, Calif. By applying network switching to hard-disk drives, startup 3ware Inc. believes it has found a way to bring ATA drives up to the same speed as more expensive SCSI drives. As the company begins shipping its first products next month, its founders believe they can help PC OEMs improve system speed through storage one of the least tapped areas for performance gains while breathing new life into ATA.
"Storage has been a critical bottleneck for computers," said Peter Abrams, director of marketing for 3ware (Palo Alto, Calif.).
Advances in ATA drives have brought them to speed parity with SCSI. But restrictions on the ATA bus cancel out that speed, particularly in multiple-drive systems. Because the bus can handle traffic for only one drive at a time, it could instruct one drive to look for data, then begin downloading data from a second drive. After the first drive has located its data, it must wait for the second to finish using the ATA bus.
Adding intelligence to the ATA drives doesn't help. "You add a lot of cost and complexity to each drive to get them to play on the same bus, and they still don't work well together," said Jim McDonald, cofounder and chief technical officer of 3ware.
3ware's answer is to use packet switching to coordinate the multiple disk drives, eliminating much of the latency created by the ATA bus. Similar ideas are being pursued in the Next-Generation I/O (NGIO) and Future I/O projects.
3ware replaces the ATA bus with an architecture called DiskSwitch. Each ATA drive is given its own data channel, a proprietary channel called AccelerATA. The combined channels feed through a proprietary transaction-control bus into a packet-switching controller, which feeds the data to the system's PCI bus and into memory.
The individual AccerlerATA channels ensure that each drive can transmit data when ready, rather than wait for the ATA bus to clear. As a result, adding drives to the system will increase the overall storage throughput without getting in each other's way.
Also on board is a 16-bit Siemens C163 processor to handle data traffic, lifting all storage responsibility from the CPU. The side effect is to speed up overall system performance.
DiskSwitch is sold as a board that can connect to as many as four drives. The operating system considers the entire setup to be one huge drive, making network management easier.
Benchmarks that 3ware has run show the DiskSwitch setup raises ATA drives to SCSI speed, even if there's only one drive in a system. The company said DiskSwitch will let OEMs boost system speed while saving the costs of SCSI interfaces.
The company's initial targets are mainstream PCs, where performance is important but setups like RAID drives are out of the question. "They will have to develop the market for upper-end capabilities," said James Porter, president of storage research firm Disk/Trend Inc. "But for those markets looking for performance, they should do a good job."
The DiskSwitch 4 boards that appear in May will be able to handle up to four drives, with eight-drive boards planned for the future. "Particularly in the server space, five or six drives is going to be the sweet spot," McDonald said.
The DiskSwitch 4 connects to a 32-bit, 33-MHz PCI bus and supports Windows NT 4.0 or 98. The DiskSwitch 4S, due in September, will add support for NetWare and Linux as well as extra administrative software and RAID options. 3ware is also working on boards for 64-bit, 66-MHz PCI, which are due later this year.
3ware claims OEMs are ecstatic to learn they can get such performance from cheap ATA drives, while disk manufacturers are happy to have a vehicle for showing off ATA advances.
"In the storage industry people talk about the peak bandwidth," McDonald said. With SCSI, "people will talk about 80 Mbytes/second. You won't get 80 Mbytes/s. You're lucky to get 10."
Besides being less costly, the 3ware solution is more scalable than SCSI. The DiskSwitch architecture raises throughput roughly linearly with each drive added, but with a SCSI bus, "as soon as you get past three drives, you flatten that curve," Abrams said.