Long Busy; Internal Disk Components; Shared Cpc Resources - IBM Multiprise 3000 Reference Manual

executed when a loop is detected. With only one transfer of command parameters
from the application program, either the desired record is found or an exception
condition occurs. A second transfer of parameters may then be needed to structure
the ending conditions for the loop, such as providing Read Count information that
points to the correct final record.
Since Internal Disk has access to the channel program and its parameters,
detection of the loops does not depend on mode settings or hints from supervisory
software.
SSID
Subsystem identifier (SSID) support is provided for the unique identification of
Internal Disk control units within a customer installation.Three fixed default values
of SSID are provided:

Long Busy

The 3990 mod 2 uses the long busy indication to indicate to the host that an
extended operation is being executed at the device. Internal Disk uses the long
busy indication in some rare instances of subsystem failure as a means for having
CCW chains redriven from the host system.
The 3990 Models 2 and 3 documentation used "State Change Pending" to describe
the condition that is called "Long Busy" in this document.

Internal Disk Components

The following section describes the basic components of the Internal Disk
Subsystem. The Internal Disk is ordered by capacity. Based on the capacity,
varying numbers of components are required.
An Internal Disk Subsystem consists of the attachment integrated in the CPC and
some number of HDDs configured into RAID arrays. The major components
comprising an Internal Disk Subsystem are the SSA adapter cards, 18GB UltraStar
18ZX disk drives, and packaging for the HDDs within the CPC frame or expansion
frames.

Shared CPC resources

The CPC provides physical mounting facilities as well as power, cooling and
service panel facilities for the Internal Disk Subsystem. Special Licensed Internal
Code (LIC) running on the System Assist Processor (SAP) performs channel,
control unit (3990-2), and device (3380-J/E/K or 3390-1/2/3/9) emulation functions
and manages a portion of the CPC memory as a subsystem read cache across all
Internal Disk Subsystem devices. The read cache capacity can range from 32MB to
2GB. The 2GB cache can only be selected on a Multiprise 3000 which has 4GB
An SSID of x'FD00' is assigned to the logical subsystem that services the disks
within the CPC frame.
An SSID of x'FD01' is assigned to the logical subsystem that services the disks
within the first expansion frame.
An SSID of x'FD02' is assigned to the logical subsystem that services the disks
within the second expansion frame.
Chapter 1. Overview of the S/390 Internal Disk Subsystem
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