
Chapter 5. 24-Byte Compatibility Sense Data
The Internal Disk sense information sends 32 bytes to the host for the following
reasons:
Identifies the cause of the last unit check status presented for the logical
volume on this channel interface.
Provides data that may be required for system error recovery.
Provides information that aids the service representative in diagnosing and
isolating subsystem malfunctions, or notifies the system operator of significant
subsystem conditions.
The sense information is presented as either
24-byte compatibility sense data
or
ECKD 32-byte sense data
. The 24-byte sense data is used for most Internal Disk
unusual conditions and for 3380 logical volume conditions. The 32-byte sense data
is used for 3390 logical volume and some Internal Disk unusual conditions.
When byte 27, bit 0 is ‘1’, the sense data is 24-byte compatibility mode format.
In
this format, the first 24 sense bytes are compatible with the 24 sense bytes of
previous attachments.
The 24-byte compatibility sense data is used to report:
All control unit equipment checks
All program checks on all logical volume addresses (format 0) except the
following nonsynchronous mode exceptions:
– End of extent with imprecise ending
– Incorrect TLF in CKD conversion mode with invalid track format
– Incomplete domain
Equipment and data checks on emulated 3380 logical volumes.
Eight additional sense bytes are appended to the original 24 sense bytes.
Therefore, the Internal Disk sends 32 bytes of sense information to the channel
when it receives a Sense command. If the Sense command is not preceded by a
unit check status for the same logical volume on the same channel interface, the 32
bytes are format 0, message 0, with sense bytes 0 through 3 equal to zero.
The Internal Disk detects some error conditions when not communicating with a
channel, or after it presents ending status for a CCW chain. The Internal Disk does
not report the error until the next channel-initiated selection. Predicted device
failures are reported in this manner.
Copyright IBM Corp. 1999
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