Digital Equipment EK-SFXXS-SG-003, Service Manual

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2
Theory of Operation
This chapter describes the normal operation of the storage enclosures and
the DECarray.
General descriptions of normal operations are presented so the service
person has a frame of reference to compare the customer complaint to a
possible service problem.
This chapter also provides guidelines that you should follow when
servicing the storage enclosures and the DECarray.
2.1 Overview
The magazine tape ISEs and disk storage enclosures in a DECarray can
be connected to one or more host systems. Possible configurations can be
broken down into three basic categories: single-system, stripe set, and
DSSI VAXcluster configurations.
In the single-system and stripe set configurations, the ISEs on a DSSI bus
connect to one system. In the DSSI VAXcluster configuration, the ISEs on
a DSSI bus connect to two or more systems, and any system can access
any ISE on that bus.
In a DECarray, using DSSI bus convention, the higher DSSI node IDs are
reserved for DSSI adapters resident in the system. The lower DSSI node
IDs are reserved for magazine tape ISEs. The remaining DSSI IDs are
used for the disk ISEs in the storage enclosures.
When correctly configured and connected, data on the DSSI bus passes to
all ISEs on the bus. The DSSI node ID passed on the bus enables the ISE
with that DSSI node ID to communicate on the bus, either receiving data
to be written to the ISE or reading data from the ISE.
2–1