Open SCSI Integrator's Manual for NonStop S-Series Servers

Open SCSI Integrator’s Manual for NonStop Servers—422988-002
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Overview
This section provides an overview of the Open SCSI subsystem, including a description
of how the various components of this subsystem operate and interface with devices
supplied by third-party integrators. It includes the following topics:
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The Open SCSI Interface on page 1-1
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The External Open SCSI Bus Interface on page 1-2
The Open SCSI Interface
The Open SCSI subsystem provides the hardware and software for a SCSI-2 open
interface that runs on NonStop S-series servers and to which developers can attach a
single small computer system interface (SCSI) device. The Open SCSI interface
includes the following components and features:
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A SCSI port connector exists on the following CRUs on the NonStop S-series
server:
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Processor Multifunction (PMF) customer-replaceable unit (CRU)
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I/O Multifunction (IOMF) CRU
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The SCSI Plug-In Card (S-PIC) on the 6760 ServerNet device adapter (6760
ServerNet/DA)
Each 6760 ServerNet/DA contains up to four S-PICs.
Open SCSI is supported on the 6760 ServerNet/DA beginning with the G06.06
software release. For information about the features of the G06.06 software
release and considerations for migration, refer to the Gxx.xx Software
Installation and Upgrade Guide.
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Depending upon the developer’s requirements, a second SCSI controller and its
SCSI port can be added to the Open SCSI bus as a backup for purposes of reliability
and additional fault tolerance.
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An Open SCSI I/O process (IOP) is supplied to support passthrough from an
application to the external device. The IOP uses Guardian procedure calls such as
FILE_OPEN_, FILE_CLOSE_ and WRITEREAD[X]. The IOP presents a standard
file-system interface to the application program, and it runs as a fault-tolerant
process pair.
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The Open SCSI IOP supports the attachment of one separately addressable and
controllable logical unit to the external device.