volumes to physical disks. A functional volume is a logical volume still defined by track size, capacity, and address. This mapping structure is contained in a series of tables stored in the control unit. These tables are updated at each write on functional volume, and have to be maintained when previously used space is released.

Data from all functional volumes could reside on one array device or many array devices. Functional volumes can be defined and configured non-disruptively through dynamic activation and utilities, such as IBM Extended Facilities Product (IXFP) for the RAMAC Virtual Array (RVA). Because more arrays can be installed and defined non-disruptively, increasing the capacity of such a control unit is easy.

Defining a logical volume by tables brings capabilities such as easy and almost instantaneous volume duplication when both source and target volumes are controlled by the same set of tables inside the same storage server. However the actual data copy has yet to take place. Either background storage server tasks or system utilities implement the movement of data. Virtual volume definition by tables brings another function: it allows the instant volume duplication by creating two independent host access views of the same data, simply sharing the same data with no replication. The IBM RVA SnapShot enables instantaneous duplication with no physical space utilization at duplication time. This advantage comes from the other architecture improvement, the LSF concept, on which the virtual volume architecture is based.

9.2 Disk Control Units

DB2 uses VSAM Media Manager for its I/O operations. Like any access method, VSAM Media Manager builds for every I/O a channel program and sends a request to the I/O supervisor. The I/O supervisor enqueues this request on a device number for the channel subsystem.

The channel program consists of standard commands, described in the ECKD disk architecture, that specify I/O demand to the control unit. The control unit executes these commands, propagates them and controls their requests to logical volumes and physical devices. It also manages data delivery to the channel subsystem.

The channel subsystem manages the transfer of channel commands and of data through links to the control unit. This linking can be complex and involves ESCON Directors, channel extenders, and even telecommunication devices for remote I/Os.

There are two views of a disk control unit. Physically it is a storage server to which disk drives are attached and the channel links from hosts are connected. The storage server contains all the facilities to perform the I/O operations. Logically the disk control unit is an aggregate of subunits known as logical control units (LCUs) or control unit images, doing the I/O operations.

9.2.1 Storage Server

The storage server contains all shared resources and processes to support LCU activities. It often consists of two or more clusters. A cluster can take over the

Disk Environment Overview

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IBM 5695-DF1, 5655-DB2 manual Disk Control Units, Storage Server
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5695-DF1, 5655-DB2 specifications

IBM 5655-DB2 and 5695-DF1 are significant components within the IBM software ecosystem, predominantly focusing on data management and integration solutions. These offerings cater primarily to enterprise environments that require robust database management systems and associated frameworks to maintain and manipulate data efficiently.

IBM 5655-DB2 is a well-known relational database management system (RDBMS) that excels in managing large volumes of structured data. Its architecture is designed to support high availability, scalability, and performance, crucial for businesses operating in today’s data-driven world. Some of its main features include advanced indexing capabilities, support for complex queries, and dynamic workload management. Additionally, it provides strong concurrency controls, which enable multiple users to access and manipulate data simultaneously without compromising data integrity.

One of the key characteristics of DB2 is its support for various data types, including JSON and XML, making it versatile for modern applications that generate data in diverse formats. It also features robust security mechanisms to protect sensitive data, aligning with compliance standards across industries. Integration with analytics tools further allows businesses to derive insights from their data, enhancing decision-making processes.

On the other hand, IBM 5695-DF1, also known as the InfoSphere DataStage, is a powerful data integration tool that facilitates the extraction, transformation, and loading (ETL) of data from various sources to target systems. It empowers organizations to streamline their data flows, ensuring that clean, consistent information is available for analysis and operational use. Key features of 5695-DF1 include a user-friendly graphical interface that enhances developer productivity and a rich set of connectors for numerous data sources, enabling seamless data integration.

DataStage also supports real-time data integration, allowing businesses to keep their data synchronized across multiple platforms. Its parallel processing capabilities dedicatedly optimize performance, enabling organizations to handle vast datasets efficiently. It incorporates data quality tools that help in validating and cleansing data before it is used for decision-making processes.

Both IBM 5655-DB2 and 5695-DF1 are part of a broader strategy to accommodate the evolving landscape of data management. Businesses leverage these technologies to enhance their data architectures, fostering agility and competitive advantage in their respective markets. Their integration capabilities, along with a focus on security and scalability, position them as vital assets in modern enterprise environments. Whether managing critical data within a database or ensuring seamless data flow across systems, these IBM offerings provide a comprehensive approach to handling complex data challenges.
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