Exception handling90
HP restricted
1. Clean the heads and try the operation again.
2. If the ‘Clean’ LED is lit again, repeat the operation with another tape cartridge. If this clears the
‘Clean’ LED, it indicates that the original cartridge is at fault. Copy the data from the cartridge
onto a new one and discard the old cartridge.
The ‘Clean’ LED is cleared by a cleaning cycle.
Providing pass-through mode
It is important for Drivers and Logical Device Managers to provide a pass-through mode that can
return information or commands specific to a vendor’s product. The need for this is two-fold:
• Systems must support a great variety of new devices.
• All tape drives are similar to a degree; Drivers and Logical Device Managers tend to provide
connectivity based on the assumption that 80% of all SCSI tape drives behave identically.
Pass-through mode offers the following advantages:
• Peripheral manufacturer can provide value-added diagnostics and support applications over
and above those that may be shipped with a system or application.
• System supervisors and operators can take advantage of specific product features otherwise
excluded because the driver or manager only caters for 80% of SCSI drives.
• Technical support people have access to low-level device-specific information likely to be
unavailable otherwise.
Requirements for drivers and logical device managers
Drivers and Logical Device Managers must allow the user to do the following:
1. Create either a 6-byte, 10-byte, 12-byte or 16-byte SCSI Command Descriptor Block.
2. Allocate a write buffer or file for any data associated with the SCSI command that will be sent to
the drive.
or
Allocate a read buffer or file for any data associated with the SCSI command that will be
returned by the drive.
3. Link the command and data buffers.
4. Launch the command.
5. The driver should use its standard
CHECK CONDITION and REQUEST SENSE routines to report
whether the command completed successfully or not. The caller must have access to the raw
REQUEST SENSE data.
6. View any returned data.
