some comments on PLDA tapes using Class 3

[Charles Monia 237-6757]

* From the SCSI Reflector, posted by:
* Charles Monia 237-6757 <monia at AM.SHRMSG.SHR.mts.dec.com>
*
Hi Ralph:

In case 4, using your recommended action how would you resynchronize tape
position?  Do you rewind and start over or backspace?

Thanks,
Charles

>
>Doug,
>
>I wouldn't write a driver to follow case 4 proposed, specifically,
>
>} case                    what the          result of         next
>}                         initiator         READ POSITION     initiator
>}                         sees              command           action
>} =====================================================================
>}
>} 4. Command and data     command           result is NEW     send next
>} succeed, but status     times out         (i.e. expected)   command
>} gets lost on the way                      value of
>} back to initiator                         position
>}
>} 5. Failure in command   command           result is OLD     re-send
>} or data, and status     times out         value of          command
>} gets lost on the way                      position
>} back to initiator
>}
>
>I'd change case 4 to read:
>
> case                    what the          result of         next
>                         initiator         READ POSITION     initiator
>                         sees              command           action
> =====================================================================
>
> 4. Command and data     command           result is NEW     a) backup
> succeed, but status     times out         (i.e. expected)   to OLD value
> gets lost on the way                      value of          of position
> back to initiator                         position          b) re-send
>                                                             command
>
>Call me paranoid, but the unexpected position result tells me only that
>the tape is not positioned where it ought to be.  Assuming that an
>unexpected position result means that the write finished successfully
>is, to my mind, wildly optimistic.
>
>Ralph...
> --

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