StorageTek 6 System Control Program SCP, Storage Management, Device Management, File Management

System Control Program (SCP)

The service virtual machine executes a proprietary System Control Program which provides a small subset of MVS services that include the following major components:

•Storage management

•Device management

•File management

•Task management

•Job management

•Processor management

•Communication

•Inter-machine communication

•Task recovery/termination.

Storage Management

The storage managed by the SCP is a single ‘‘real’’ storage range; no virtual storage management is performed. The maximum amount of storage that is available to a user is 16 megabytes, but in actual practice 8 megabytes may be sufficient. Any paging or page faults are managed by VM and are transparent to the virtual machine. The SCP associates storage keys with ‘‘JOBS’’. VM job steps are mapped to unique storage keys. Storage Management is a matter of managing available storage and allocating and deallocating storage through standard macro calls.

Device Management

This component has exclusive control over SCP driven I/O activity to virtual devices. IUCV is the interface to the DASD data sets which are accessed through requests to the CP BLOCKIO service (using device I/O mainly for the Reserve-Release mechanism). Other devices include several spool files for console, diagnostic, and performance logs, and DASD I/O for minimal use. Also included with this component is the function of logging unsuccessful attempts to log errors to the Error Recording Data Set (ERDS).

File Management

The SCP supports several access methods:

•Sequential (BSAM/QSAM) for spooled unit record input/output and DASD input/output

•Direct (BDAM) for data base manipulation.

BSAM/QSAM is supported through EXCP processing of channel control word (CCW) chains. BDAM files are accessed through IUCV communication to CP DASD BLOCKIO. The requests are converted from a relative block to a physical block on DASD which is passed to BLOCKIO.

No DASD file allocation is performed. All DASD data sets must be preallocated OS-format data sets or CMS ‘‘reserved’’ minidisks.

Chapter 1. System Description 7

1st ed., 6/30/04 - 312579601