
The extended parameter field must be one byte in length (byte 20 only). This byte
specifies the set size used in the Locate Record Extended domain. The track set
size must be ‘1’ (the device value returned in byte 47 of the Read Device
Characteristics command response). If the track set size byte is other than ‘1’, the
command is rejected with unit check status. The sense data contains command
reject with format 0, message 4.
Notes:
1. Extent checking is performed during the validation of Locate Record Extended
parameters, not during track access.
2. The sector number parameter is not used.
Track access is initiated using the seek address parameter.
If the file mask inhibits all write operations, Locate Record Extended is rejected with
unit check status. The sense data contains command reject with format 0,
message 2.
When track access is complete, the control unit orients to the beginning of the
count area of a user record and prepares to update write the associated record.
The search argument is ignored and no search operation is performed. If no data
record is found within the track, the command is rejected with unit check status.
The sense data includes No Record Found. If no data is found in the accessed
track, the operation is rejected with unit check status. The sense data includes No
Record Found.
When auxiliary byte, bit 7 is ‘0’, Locate Record Extended must be followed by the
number of Write Update Data commands sufficient to process the specified number
of records in the count parameter. When the auxiliary byte bit 7 is ‘1’, the Locate
Record Extended command must be followed by a number of Write Update Data
commands that is one less than the value specified by the count parameter and the
last channel command in the Locate Record Extended domain must be a multitrack
Read Count command.
If an invalid command sequence is detected within the Locate Record Extended
domain, the invalid command will be rejected with unit check status. The sense
data contains command reject with format 0, message 2.
If the operation continues past the last record updated on the track, control unit
orients to the beginning of the count area of the first data record on the track and
prepares to operate on that record.
If the number of write commands exceeds the number of data records on the track,
one or more of the data records updated in the Locate Record Extended domain
will be written again. No exception is reported.
If the data area length of any updated record differs from the value in the transfer
length factor (TLF) or the blocksize parameter from the Define Extent command (if
no TLF was specified), processing is rejected with unit check status and the record
is not updated. The sense data includes Invalid Track Format.
The record ID of the first record is contained in the first count field, or can be found
by suffixing a Read Count command to the Locate Record Extended domain.
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Internal Disk Subsystem Reference Guide
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