DEC-SDI-DiskControllers

This document describes Digital's SDI (Standard Disk Interconnect) Disk Controllers, intelligent microprocessor-based controllers designed for RA-series disk drives and Storage Arrays.

The primary aim of SDI controllers is to maximize I/O performance and data reliability while reducing host CPU overhead. They achieve this by offloading disk I/O control functions from the main CPU, allowing the CPU to focus on application-oriented tasks.

Key features and benefits include:

• Performance Optimization: Utilizing built-in algorithms like seek ordering, overlapped seeks, and rotational optimization, SDI controllers significantly increase throughput without consuming host CPU cycles. They offer high I/O-per-second rates, with recent microcode enhancements providing up to 60% performance improvements in specific applications.
• Robust Data Integrity: Extensive features ensure data availability and reliability, including an industry-leading 170-bit Reed-Solomon Error Correction Code (ECC), Error Detection Code (EDC) to verify data paths, and proactive Bad Block Replacement (BBR) to anticipate and correct media defects before data loss occurs. Quadruplicate headers and single-point failure detection further enhance data safety.
• System Integration & Flexibility: Designed as part of Digital Storage Architecture (DSA), the controllers interact with the operating system via the Mass Storage Control Protocol (MSCP), eliminating the need for unique device drivers and promoting device-independence. The SDI's radial connection scheme ensures that the unavailability of one drive does not affect others, enhancing overall system availability. Each controller can support up to four RA-series drives or components, offering flexible and expandable storage configurations.
• Architecture & Models: The controllers feature a dual-microprocessor architecture, decoupling drive-controller data movement from controller-host data movement for configuration flexibility. Digital offers specific models: the UDA50 for UNIBUS systems, the KDA50 for Q-bus systems, and the KDB50 for VAXBI systems, each tailored to its respective bus while providing core SDI benefits.
• Ease of Maintenance: Equipped with extensive onboard diagnostics and utilizing Field Replaceable Units (FRUs), SDI controllers facilitate quick and accurate fault identification and repair, reducing system downtime.

In essence, SDI Disk Controllers provide a highly intelligent, efficient, and reliable storage solution that significantly improves overall system performance and data integrity for Digital's RA-series disk drives.