Chapter 3. Error Sense Information
Sense Data
For a description of Sense data, see “Sense Data Format” on page 60.
Sense Data Management
The drive maintains three types of Sense data:
Current Sense
The Sense data associated with the last command received from the
initiator.
Deferred Sense
The Sense data from a command that has been reported as Good, but has
generated sense data after being reported. This may be a command with
the Immediate flag set or may be a buffered write. A command with the
Immediate flag set generates sense for the server that sent the command.
A buffered write may generate sense for all servers.
Unit Attention Sense
The Sense data generated by a Unit Attention condition. (See “Unit
Attention Conditions” on page 87.) This is generated for all servers. When a
Unit Attention condition has been driven by a command (for example, when
mode parameters have changed), a Unit Attention is posted for all initiators
except the one that caused the change.
Any command other than a REQUEST SENSE command or an INQUIRY command
generates Check Condition status if there is Deferred Sense data or Unit Attention
data available. All commands generate Check Condition status if the command itself
generates sense data. If the next command after the Check Condition status is not
a REQUEST SENSE command, then all the sense data for that initiator is cleared.
When a REQUEST SENSE command is received, the Current Sense is returned. If
there is no Current Sense, the Deferred Sense is returned. If there is no Deferred
Sense, the Unit Attention Sense is returned. If there is no Unit Attention Sense,
default sense data is returned. Once a particular set of sense data has been
returned, that sense data is cleared. Any other sense data that is still pending may
still cause Check Condition status for subsequent commands.
Unit Attention Conditions
The drive generates a Unit Attention condition under the following circumstances:
v Reset condition (for example, power-on, SCSI reset, bus device reset)
v Tape Loaded condition (for example, media inserted, LOAD command from
another initiator)
v Mode parameters changed by another initiator
v Drive firmware has been upgraded
The drive only maintains one Unit Attention condition at any one time for any one
initiator. If a subsequent Unit Attention condition is generated, it replaces the
existing one if it is of higher priority. If it is of lower priority, it is ignored. The
priorities are in the order listed above, with a reset being highest priority and a
firmware upgrade being lowest priority.
© Copyright IBM Corp. 2001, 2000 87
