IBM Multiprise 3000, Reference Manual

Page: 57 / 264

When operating with read intent, an incomplete Domain exception will not be
reported. The Internal Disk Subsystem will threshold unit checks for Incomplete
Domain exceptions. See “Nonsynchronous Operations” on page 4-19.
Search Operation: Certain Locate Record operations need orientation to a
specific record or record area before data transfer starts. Orientation is done by a
search operation.
When specifying index orientation, the device positions to index, but no search
operation is performed.
When specifying count or data area orientation (byte 0, bits 0 and 1 are ‘00’ or
‘10’), the search argument value (bytes 8 through 12) is compared with the
count-area record ID field of each record, including record zero, after the device
is at the proper sector. When the search operation starts, it continues until an
equal compare occurs, or until all record IDs on the track have been
processed. If no record ID on the track compares equal to the search
argument, the command is terminated with unit check status. The sense data
includes No Record Found.
When specifying home address orientation (byte 0, bits 0 and 1 are ‘01’), the
search argument (bytes 8 through 11) value is compared with the track address
field in the home address. (Byte 12 is not used.) If the comparison is unequal,
the command is terminated with unit check status. The sense data includes No
Record Found.
Nonsynchronous Operations: Nonsynchronous execution of write operation
implies transferring data from the channel to the Internal Disk and advancing the
channel program before the data is actually written on the disk subsystem.
Channel end status for each write command is presented after data transfer from
the channel is completed. If another write command is expected in the Locate
Record domain, device end status is presented together with channel end;
otherwise, device end status is presented when the write operation is complete at
the logical volume.
Channel command chaining flags on write commands are monitored in the domain
of the Locate Record. If chaining ends before the count of write commands is
exhausted, an Incomplete Domain exception condition is noted and the channel
program is immediately synchronized with the logical volume. The chaining flags
will usually provide an early indication of an Incomplete Domain exception, so that
the Internal Disk Subsystem can present channel end, harden the data from cache
to the disk subsystem, and then present device end. There are several cases
where the chaining flags indicate that chaining is to continue but the chain ends.
Several types of Incomplete Domain exception can arise:
An Incomplete Domain is detected. If no subsequent exception condition arises
when writing the data to the logical volume, the next channel program to that
logical volume may be rejected with unit check status, subject to thresholding.
The sense data contains command reject with incomplete domain (byte 0, bit
7).
If an Incomplete Domain exception condition is detected before final status is
presented for the last command in the chain and a subsequent exception
condition prevents data from being successfully written to the logical volume,
the channel program is immediately terminated with ending status that includes
unit check. The associated sense data describes the error that prevented the
Chapter 4. Command Descriptions
4-19