Ultra3 SCSI Powers The Market.
This article is the second in a two-part series. The first part appeared in the June issue of CTR.
Apart from the increased bandwidth, the server market should greatly benefit from the addition of manageability features into the interface. These include Domain Validation and CRC.
Domain validation traps many operating problems that would normally prevent devices from being available to dependent applications. Once a problem is spotted, domain validation allows the device to operate in a different, perhaps slower mode, in order to help make the device available to applications. The IT professional managing the server can connect his old disks to the new host adapter without having to worry about compromising availability--domain validation attempts to do what is necessary to keep devices operational.
The sophisticated 32-bit CRC scheme makes the interface considerably more reliable than was possible with parity protection. It ensures data integrity by also detecting the probabilistically very rare occurrence of a double bit error that the old parity scheme cannot detect and thus "bullet proofs" hot plug and hot swap procedures that are now becoming standard in this market.
In addition to these manageability features, the technical community is also finishing up a major overhaul of the protocol known as Packetization. This effort primarily reduces command overheads that are beginning to account for more of the 110 overhead at the increased clock speeds that some SCSI enhancements require.
Packetization is now combined with another feature called Quick Arbitration (QA), which significantly reduces overhead associated with arbitration. These features are more useful when the bus is close to saturation and in multiple drive configurations. Servers use increasingly larger system caches that result in bigger page files, increasing the chance that the storage side I/O bus is going to saturate. RAID environments are now increasingly standard server fare and require supporting multiple disks.
The products highlighted in the STA roadmap, including expanders, LUN bridges, hubs, switches, improved cabling, and backplanes, also primarily benefit the server market. They allow SCSI to scale up and work in new configurations made possible by the adoption and support of centralized storage, clustering, and SAN technology for numerous application arenas.
The server market also benefits from other initiatives like the SCSI Accessed Fault Tolerant Enclosure (SAFTE) monitoring, SCSI Enclosure Services (SES), and SCSI Command Services (SCS) that allow for the Standardization of Storage and RAID management functions.
As these appear in products, they will allow users to manage all heterogeneous storage components easily from one utility, thereby significantly adding to the usability and manageability proposition.
SCSI is the de facto standard for branded workstations and dominates this market. It is perceived as being more reliable by virtue of being used in the server market. However, the workstation market has very different characteristics than the server market.
The end user for this segment is the highly skilled, specialized worker. Productivity is the primary concern and therefore users look for reliability in addition to performance. The server market's emphasis on hot plug, enclosure management, clustering, and investment protection do not apply to this market. Availability is less important and although RAID is used in this environment, the primary motivation is performance gain from striping (RAID 0). Because of the increased emphasis on performance and less so on availability, often the workstation market adopts new technology earlier than the server market.
The highly skilled specialized worker uses specialized applications that generate large files and therefore can experience I/O bottlenecks. This is even truer with the increasing use of RAID and striping. Thus, the workstation market should benefit from the bandwidth increase that the roadmap promises. In addition, workstations in the corporate and business environments are managed by IT professionals who will benefit from the new manageability features when troubleshooting problems and making configuration changes.
The desktop market closely resembles the workstation market, but it has several key distinctions. It is a more price sensitive market and the end user is the general corporate office worker, small business employee, or home user. Due to the cost proposition, the dominant disk interface is not SCSI. However, SCSI is still widely used by the power user who needs performance and connectivity beyond a single boot disk. Power desktop users use SCSI primarily for the following three reasons:
1. Access to best-of-breed peripherals such as scanners with the best optical technology, 8X CDRs, and Jaz drives. ATA cable limitations do not allow for external peripheral attachments.
2. Pure hard disk performance. The fastest disks are usually SCSI. They also are the most reliable, since SCSI disks are primarily used for servers in mission-critical environments. Hence, testing is more rigorous.
3. SCSI allows access to sophisticated configurations and applications such as web based, multimedia, printing and CD distribution. Hence, it helps increase general productivity.
Even with ATA's performance upgrade to UDMA/66, SCSI in the desktop environment is expected to grow at a steady 8% CAGR for the next few years, according to IDC. In fact, market research shows that more users would use SCSI if they understood the benefits.
Apart from increased bandwidth, domain validation and CRC should make SCSI devices even more attractive to this market. Specific products are also being targeted for this market, including flexible cables and a lower cost 25 pin synchronous connector for the desktop market. SCSI has a great future in all three market segments and newly announced SCSI Trade Association initiatives should significantly enhance end user experience across all three segments.
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|Title Annotation:||Technology Information|
|Publication:||Computer Technology Review|
|Date:||Jul 1, 1999|
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