CHAPTER 4: Installation and Configuration

4.5 Multiple Initiators and Clustering

A multiple-initiator environment is one in which the SCSI bus has two or more host adapters. To work in a cluster, the host adapters must perform properly in such an environment—by not resetting the bus without an explicit host command, for example. Our Ultra2 LVD SCSI Host Adapters are built for multi-initiator operation and adhere strictly to the SCSI standard.

Figure 4-6 on the next page illustrates the principal components in a cluster’s I/O system. It shows a simple cluster with two servers sharing access to online storage (the basic model for Microsoft’s MSCS clusters). Both servers contain an host adapter that provides access to the shared extemal I/O bus. Servers can share disks or arrays attached to this bus. The operating system controls contention for disk access by either resolving access conflicts with a component called a distributed lock manager (DLM) or using a so-called “shared-nothing” model that partitions disks and arrays, giving each server control over a subset of the storage under normal circumstances. MSCS uses the shared-nothing approach.

In such applications, multiple initiators can be used on a single SCSI bus. The bus is configured to have more than one host adapter inserted into at least two distinctly different computer systems sharing peripheral devices. In these circumstances, it is possible to have one of the two computer systems turned off. Under these conditions, the host adapter has a jumper that can be enabled (closed) to set the active on-board termination ON all the time, regardless of whether power is applied or not (refer to Section 3.4). The host adapter is shipped without the jumper installed, and this setting need not be changed in most cases. Before operating such a system, visually inspect the configuration you have installed to verify that all cables have been inserted correctly.

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Black Box SCSI-2 LVD manual Multiple Initiators and Clustering
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SCSI-2 LVD specifications

The Black Box SCSI-2 LVD (Low Voltage Differential) represents a significant advancement in data storage and connectivity technology, particularly in environments requiring high performance and reliability. As a variant of the SCSI (Small Computer System Interface) standard, it is optimized for faster data communication, essential for modern computing needs.

One of the main features of SCSI-2 LVD is its capability to handle increased data transfer speeds compared to its predecessors. It supports a maximum data transfer rate of up to 80 MB/s, which is double that of the original SCSI-2 single-ended signaling. This increase in speed is largely due to the differential signaling that LVD employs, allowing for reduced electromagnetic interference and extended cable lengths while maintaining signal integrity. The technology effectively converts the SCSI bus into a more robust system that can accommodate various devices without compromising performance.

The SCSI-2 LVD standard is backward compatible, meaning that it can interface with older SCSI devices, albeit at reduced speeds. This compatibility is significant for users looking to upgrade their systems without discarding existing hardware. This makes SCSI-2 LVD an attractive choice for enterprise environments where legacy systems are common.

Another key characteristic is the flexible cabling options provided by SCSI-2 LVD. It can support cable lengths of up to 12 meters, which is beneficial for large data center configurations where space between devices can be substantial. This extended range does not typically come at the expense of performance, ensuring that data integrity remains high, even over longer distances.

In terms of technology, LVD employs lower voltage levels, which not only contributes to greater power efficiency but also minimizes heat generation in devices. This is particularly crucial in data centers where temperature management can impact hardware longevity and reliability. The combination of lower voltage use and differential signaling makes SCSI-2 LVD well-suited for high-density environments.

Error correction and handshaking features are also integral to SCSI-2 LVD, enhancing its robustness against data loss during transmission. These characteristics make it a reliable choice for applications requiring consistent and high-speed data access, such as server arrays and high-performance computing tasks.

Overall, Black Box SCSI-2 LVD stands out due to its impressive speed, compatibility, and extensive cabling options, positioning it as a reliable solution for demanding data environments. It effectively bridges the gap between legacy systems and modern technology, ensuring that users can optimize their data handling capabilities without significant disruption.
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