Serial ATA: opening new markets for ATA RAID - Serial ATA

Computer Technology Review, Nov, 2002 by Mike Wentz

In addition to all of the benefits of the cable and signaling techniques, there is an additional feature of SATA that tends to get overlooked: for the first time, the connection between the drive and the controller is point-to-point instead of a bus. For every drive, there is a dedicated cable that connects it to the controller. This will dramatically change the way storage is configured and deployed because a point-to-point connection topology enables the use of switched controllers that will be able to extract much higher performance from ATA drives.

Why? Because a switched architecture enables concurrent access to all the drives, allowing for performance aggregation not possible under a bus-based architecture. Further, a point-to-point, switched architecture dramatically increases drive isolation, thereby minimizing cascading error effects that can render a bus-based system inoperable.

Bottom line: A SATA RAID controller implemented using a switched architecture will have very-high-performance, low latency, great fault isolation, may be obtained at a lower cost, and will have all benefits of SCSI RAID.

Reaping the Benefits of Redundant Storage

So, let's get back to the issue at hand: What does the availability of SATA drives and controllers mean to SCSI?

It depends on whom you ask, but most people do not believe SATA is a direct competitor for SCSI, for many of the reasons listed above: SCSI is faster and more reliable, and is the incumbent in the data center where it enjoys a good reputation.

However, SATA, especially RAID SATA, creates some intriguing opportunities for inexpensive, reliable storage for classes of data that have traditionally not reaped the benefits of redundant storage. For example, if you look at a typical server and the data stored on it, you will generally find: Financial and inventory data is stored on SCSI RAID; everything else may or may not be on SCSI, but it is certainly not RAIDed--home directories, archives, video data, file servers, etc. are all subject to loss of data due to a disk crash.

This, then, is the opportunity for SATA--to protect all data with RAID. With SATA, all of your corporate and personal data can be inexpensively protected from a disk crash. This market is far, far larger than the current market for SCSI RAID. Thus, SATA will not so much compete with SCSI, as extend the benefits of RAID into new markets.

Yes, there will be areas where SATA competes head-to-head with SCSI. The current state of the economy is providing much of the impetus behind this movement--customers need the benefits of RAIDed storage, but they simply cannot afford the cost of SCSI, so they are open to alternatives. ATA, especially with the advances in ATA RAID mentioned above, is now being successfully deployed in traditionally SCSI-only applications. And, as customers try ATA RAID and become comfortable with it, they are more willing to try it in more applications.

However, there are significant markets where SATA will pioneer RAID:

Corporate files servers storing non-critical data: The low cost and good reliability of SATA RAID makes this an ideal solution for insuring all data is protected by the benefits of RAID. Home directories, email servers, and corporate file servers can all be RAIDed with SATA technology to provide better data availability at a low cost.