Adaptec Seamless Streaming™Technology Maximizes Ultra320 SCSI Performance
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Seamless Streaming SCSI
Seamless Streaming Technology Products

Introduction   top of page

Ultra320 SCSI employs many fresh design features to deliver a new order of I/O speed. Adaptec's innovative Seamless Streaming Technology boasts advances that allow enterprise servers and workstations to achieve the full performance potential of Ultra320 SCSI data throughput.

Adaptec's new Seamless Streaming Technology pushes the performance of Ultra320 SCSI to its theoretical limit by implementing in hardware three key new design advances:

  • Ultra Streaming Data Path
  • Matrix Command Management
  • Rapid Packet Protocol Engine

These features are being introduced on the AIC-7902 Ultra320 SCSI ASIC, a dual-channel chip that is the foundation for a broad family of Ultra320 SCSI and SCSI RAID controllers, including the Adaptec 29320 and 39320 lines of SCSI host bus adapters, released in October 2002.

This white paper briefly describes how Adaptec's Seamless Streaming Technology works to optimize Ultra320 SCSI performance. Seamless Streaming Technology is designed to maximize the high data transfer rates of Ultra320 SCSI and meet the needs of both follow-on SCSI generations and the requirements of emerging high-performance I/O technologies.

Seamless Streaming SCSI   top of page

As SCSI generations have advanced in speed and capability, new design solutions have had to be devised to extract the highest possible real-world performance out of the industry standard specification. In order to achieve the maximum possible data throughput of Ultra320 SCSI, Adaptec has designed a hardware engine that goes beyond the limitations of current Ultra160 SCSI implementations to take full advantage of the performance potential of the newest generation SCSI specification. Embedded in the architecture of the Adaptec AIC-7902 PCI-X to dual-channel Ultra320 SCSI ASIC are hardware engines and designs that provide performance advantages over standard Ultra320 SCSI implementations.

Ultra Streaming Data Path
The obvious advantage to higher-speed SCSI transfer rates is the increased data throughput between the host bus and the SCSI bus. However, there have always been certain latencies associated with the overhead tasks of managing the data path from one bus to another. With Ultra160 SCSI, for instance, a new transfer cannot begin until an active transfer is complete, requiring multiple steps. Plus, command and status phases are accomplished in relatively slow asynchronous mode, and are limited to a single transfer per connection. Ultra320 SCSI eliminates these latencies.

Ultra320 SCSI packetizes commands, data, and status information, and transfers them at synchronous speeds. This improves performance by maximizing bus utilization and minimizing command overhead because multiple commands can be transferred in a single connection and at higher speeds. It also eliminates latencies in the disconnection, bus free, arbitration, and reselection phases. Now it is possible to initiate a new context on the bus immediately after the previous context - if the data path allows.

Adaptec's Seamless Streaming Technology uses Ultra Streaming Data Path to provide full streaming of command packets. Ultra Streaming Data Path optimizes performance by enabling a new transfer to begin on the bus before the active transfer has finished. This allows commands to be streamed to both buses, allowing each to operate at peak efficiency to deliver full Ultra320 speeds.

Such streaming performance has not been possible before. Conventional designs that worked well for Ultra160 SCSI will create performance issues when applied to Ultra320 SCSI. Unless the design takes full advantage of the speed potential of the Ultra320 SCSI specification, the speed delivered by Adaptec's Ultra Streaming Data Path is not attainable in other SCSI implementations.

Adaptec's AIC-7902 with Ultra Streaming Data Path virtually eliminates the overhead associated with establishing a solid SCSI connection, enabling the bus to take full advantage of packet protocols and deliver its maximum throughput speed.

Matrix Command Management
Ultra320 SCSI poses new design challenges in managing SCSI commands. New command-management methods are required to realize the full performance potential of the specification since it incorporates new capabilities that require a different way of handling commands. In an Ultra160 SCSI bus, for each new command the SCSI connection must be completely closed, then re-established, the command retrieved, then sent, and the entire process repeated for each command. Because the Ultra160 SCSI bus could only handle a single command per connection, there was plenty of time to retrieve individual commands. Not so with Ultra320 SCSI.

Command management has become a critical performance issue because each Ultra320 SCSI channel can accommodate up to 512 different packetized commands in synchronous mode. This means that commands now can flow to the bus as rapidly as bus processing will allow - if there is a mechanism for organizing and retrieving the commands quickly enough.

To ensure the fastest possible execution of all SCSI commands on the Ultra320 SCSI bus, Adaptec has developed a unique Matrix Command Management approach that enables command streaming in the AIC-7902 chip.

Adaptec's Matrix Command Management provides a sophisticated hardware-based method of organizing and retrieving the more than 1,000 SCSI commands required for the dual channel Ultra320 SCSI AIC-7902 ASIC. This proprietary queuing arrangement enables the streaming delivery of all the commands for a specific target. With Adaptec's Matrix Command Management, all 512 SCSI commands are immediately available for indefinite streaming to every device on each channel.

Rapid Packet Protocol
One of Ultra320 SCSI's chief benefits is that packetization allows multiple commands, multiple data blocks, and/or multiple status blocks to be transmitted during a single physical connection. However, in order to realize the complete 320MB data transfer speed, packetization must be carried out as efficiently as possible. At Ultra320 SCSI data transfer speeds, any software intervention to perform command management would reduce overall throughput. Adaptec's Seamless Streaming Technology features Adaptec-designed, dedicated hardware engines that automatically handle the packet protocol.

Adaptec's Rapid Packet Protocol (RPP) provides dedicated hardware engines for the specialized handling of SCSI protocol packets. Adaptec's RPP sends commands to a target, receives status packets from a target, and transfers data to and from a target - all at the theoretical maximum speed of 320 MB across the SCSI bus. With RPP, Adaptec's Seamless Streaming Technology delivers the fastest and smoothest transmission of multiple commands in a single connection.

Seamless Streaming Technology Products   top of page

Adaptec's Seamless Streaming Technology is the foundation of a range of Ultra320 SCSI solutions from Adaptec. Introduced in the AIC-7902 ASIC, Adaptec's Seamless Streaming Technology will be incorporated in a variety of Ultra320 SCSI and Ultra320 SCSI RAID controllers to begin launching in early 2002.

The AIC-7902 dual-channel Ultra320 SCSI chip supports all major operating systems and offers a forward pin-compatible path from the Adaptec AIC-7899W for easy migration from Ultra160 to Ultra 320 SCSI. For robust data protection, the AIC-7902 features embedded hardware mirroring and supports RAID levels 0, 1, and 1/0. The ASIC also supports Adaptec's unique Embedded RAID Logic (EMRL) technology to provide the lowest risk transition path to Ultra320 SCSI RAID for high-density servers now using zero channel technology.

The AIC-7902 with Seamless Streaming Technology is also deployed on the Adaptec 39320 SCSI card, Adaptec's new Ultra320 SCSI host bus adapter. This next-generation 64-bit/133MHz PCI-X to SCSI card supports up to 30 SCSI devices across two Ultra320 SCSI channel to provide 640 MBps of SCSI bandwidth. The 39320 also sports two external very high-density connector interfaces (VHDCI) and one internal high-density 68-pin connector to provide users with a wide variety of connection options.

Conclusion   top of page

Adaptec's Seamless Streaming Technology gives users a performance edge in Ultra320 SCSI by innovatively exploiting the full performance potential of the standard's specification to deliver the theoretical maximum data throughput speed. Seamless Streaming Technology also provides an advanced performance foundation for both future generations of SCSI, and emerging high-performance I/O technologies such as Serial Attached SCSI.

Look for Seamless Streaming Technology throughout Adaptec's growing family of Ultra320 SCSI solutions, and future iterations of leading-edge I/O solutions.

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