Chapter 1. Overview of the S/390 Internal Disk Subsystem
This chapter gives an overview of the S/390 Internal Disk Subsystem, describes its
components, features, and facilities.
Internal Disk storage subsystem provides internal attachment of disk storage
integrated into the Central Processing Complex (CPC) of a S/390 CMOS processor.
Internal Disk consists of attachment hardware and microcode plus high capacity,
high performance Hard Disk Drives (HDDs) that are packaged under the same
CPC covers. The HDDs are organized into RAID arrays that insure data availability
while minimizing the cost of disk storage. The HDDs appear to the host programs
executing in a CPC as conventional Count, Key, Data (CKD) disks attached to a
CKD control unit. The programs use channel commands to manage the operations
of the disk subsystem.
The control unit and channel functions are executed within the CPC utilizing
processor and memory resources of the CPC:
A System Assist Processor (SAP) is used for the channel emulation and control
unit functions.
Disk cache space is allocated from S/390 main memory
The system Service Element (SE) is shared for configuration and service
functions.
Power, packaging, and cooling are all provided by the Multiprise
3000 (host
processor).
From an implementation perspective these functions are an extension to the I/O
subsystem within the CPC.
Unique to the Internal Disk subsystem are Hard Disk Drives (HDDs) and logic cards
that carry adapter electronics. The logic cards are called SSA adapter cards. The
Hard Disk Drives (HDDs) used in Internal Disk are 3.5 inch, fixed block disk drives
with a data capacity of 18 GB. The SSA adapter card interfaces to the Multiprise
3000 via a PCI bus and provides an industry standard SSA (Serial Storage
Architecture) interface for connection of the HDDs.
The HDDs are mounted in the frame used for the packaging of the CPC. The
18GB UltraStar 18ZX drives are mounted in the HDD enclosure. The user may
choose to expand the storage beyond the capacity of the CPC frame by adding
expansion frames. The maximum configuration has one CPC frame and two
expansion frames.
The Multiprise 3000 has a minimum Internal Disk capacity of 72GBs and a
maximum capacity (inclusive of two expansion frames) of 792GBs.
The Internal Disk Subsystem offers the following advantages:
Minimization of software changes: If an operating system supports the device
being emulated, the Internal Disk subsystem can generally be installed without
any system software changes. Any combination of 3390-1, -2, -3, -9, and
3380-J, -E, -K logical volumes can be created on a RAID array. The total
number of logical volumes that can be created is only limited by the storage
capacity available on the array and the number of unit addresses that can be
assigned to an array. The latter one is 64 for an array with 5 HDDs (4+P), and
Copyright IBM Corp. 1999
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