IBM System/370 Guide

3. When a seek malfunction is detected.
The control unit retries the command ten times in an attempt
to position the arm correctly.
q. When an alternate or defective track condition is recognized
before data transfer begins.
The control unit determines the location of the alternate or
defective track (from RO on the track), initiates a seek to
this track, and orients to the index point. When this sequence
completes, the original command is reissued by the control unit.
This is a programmed procedure for previously announced
System/360 direct access devices.
5. When a command overrun (or late command chaining) condition
occurs during execution of a channel program because of
interference from another channel or the CPU.
The control unit initiates a retry of the command that was late.
Error logging. Usage and error counters for each drive in the facility
are maintained continuously in the control unit. The usage counters
are used to accumulate the number of bytes read and seeks issued.
The error counters are used to accumulate the number of seek,
correctable data, and uncorrectable data errors that were retried
successfully by a command retry procedure, as already described. When
a counter reaches its threshold or when a pack is removed from a drive,
the control unit indicates the condition via a unit check when the
next I/O operation is initiated to the drive. Counter data can be
obtained and counters can be reset by issuing a SENSE or READ LOG
command. These statistics can then be logged in the system error data
set for later diagnosis.
Inline diagnostic tests. The 3830 control unit can execute diagnostic
tests on a malfunctioning drive while normal operations take place
on the remaining drives in the facility. When the CE inserts the
service address plug in the malfunctioning drive, diagnostic programs
contained on a magnetic disk cartridge are read by the device in the
control unit. Diagnostics can be executed on that drive by the customer
engineer using the CE panel on the 3830 control unit. Operationally,
the drive is offline to the control unit, and physically, the drive
is offline to the operating system.
Online testing of the 3330 facility can be performed under OLTEP
control as usual. Both OLT's and diagnostic programs contained in
the OLT library can be executed on a malfunctioning drive via OLTEP.
The diagnostic tests are loaded into control storage in the control
unit from the OLT library. Operationally" the 3330 drive is online
to the control unit but is logically offline to the operating system.
Inline and online testing allows CE diagnosis and repair of most
3330 failures without the necessity of taking the entire 3330 facility
out of the system configuration.
The 3330 facility offers more than additional capacity, fast access,
and attractive price performance. The 3330 facility is actually a
subsystem in itself. The control unit can control the concurrent
execution of one RPS channel program on each of its drives and can
handle functions, such as error correction and logging, that normally
must be programmed, thereby relieving the control program of these
activities. In addition, the availability and serviceability of the
3330 are improved by the implementation of new automatic error
correction features, by use of inline diagnostics, and by the speed
qO

IBM System/370 Specifications

General

Brand	IBM
Model	System/370
Category	Server
Language	English