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Page 6
Disconnect/Reconnect Function
Early Warning Function
Error Reporting
When the drive is performing a task not requiring communication with the Initiator or
when the tape drive determines that a relatively long time has passed with no bus
activity, it disconnects from the SCSI bus. Examples are:
•
When rewinding the tape.
•
When writing to the tape and the buffer is full.
•
When reading from the tape and the buffer is empty.
•
When spacing, locating, or generally performing any tape motion when data
cannot be transferred on the SCSI bus.
During the time the Target is disconnected for one of these functions, the bus is free
for use by other devices. Both disconnect and reconnect are initiated by the Target.
If the tape drive is selected while disconnected, it only allows the following actions:
•
If the command is from a different initiator or is from the same initiator but to a
different LUN, the tape drive accepts the command and immediately disconnects
if the command is a media-access command. If the new command is a Request
Sense, Inquiry or Test Unit Ready, then the new command is executed
immediately.
•
Immediately following the selection, the Initiator may send the Identify, No Op,
Abort, or Bus Device Reset messages to the drive.
•
If the command is from the same initiator to the same LUN, the current
command terminates with a Check Condition and an Abort Sense Key.
Early Warning on the Viper drive is a logical warning given when 64 megabytes of
storage space remain on the tape. The position is calculated by the drive. When this
physical position is reached on a tape, the following occurs.
1.
Data transfers from the host are terminated at the next disconnect burst size
boundary for SEW=1.
2.
All data remaining in the drive buffer is written to the tape if SEW=1.
3.
The command completes with a Check Condition and a 40h Sense data mean-
ing EOM and no Sense Key.
4.
Subsequent WRITE commands write data and complete with check condition
with EOM Status and No Sense Key until the physical tape end is encountered.
Soft errors are generally tape-quality related and occur more frequently during write
operations than during read operations. Soft errors indicate repeated attempts by the
drive to read or write data on the tape. Some soft errors are normal, but an increase
in the usual count can indicate deteriorating tape quality. If the soft error count
LTO SCSI Interface Manual
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