On Monday, 15 November 1999 at 11:01:05 -0800, Matthew Jacob wrote:
>
>
> On Mon, 15 Nov 1999, Rodney W. Grimes wrote:
>
>>>
>>> Reread/reresponse, sorry- ENOCOFFEE:
>>>
>>>
>>>>>
>>>>> 1 filemark can not be used for EOT, it is EOF, you can't tell if what you
>>>>> read next is another file or not that may have been left by a previosly
>>>>> longer usage on the tape.
>>>>>
>>>
>>>
>>> Well, read until *BLANK CHECK* seems to be what the driver can and should
>>> do. Let me ponder this some- I believe what I propose actually works fine
>>> for all the devices we currently support (hell, I use it all the time
>>> myself). If you can provide an actual example of a SCSI tape device that
>>> if you take FreeBSD-current or FreeBSD-3.3 and do a 'mt seteotmodel 1' on
>>> and *not* be able to detect EOT, let me know!
>>
>> You won't get ``blank check'' if the tape has previosly been written
>> past where you just finished writing. Instead you often get trash.
>
> Sorry, no. When you write a tape with these devices there's always a
> leading erased area. That's why if you overwrite the front a tape you
> can't skip past this area to recover data you really need. A misfeature of
> modern technology.
Is this anchored in the standards? What about DLT? What about future
drives? I certainly wouldn't rely on anything that isn't guaranteed
to stay that way. What happens if I write a tape on FreeBSD and read
it in on System V?
>> In your other message you talk about the driver getting 2 residuals
>> in a row, well, unless you write the 2 EOF's you won't always get that...
>> depends on if the tape drive does it automagically (which many newer
>> drives do, they write 2 eof's and backspace over 1 of them for you when
>> ever you tell them to write EOF, the drive itself uses 2 EOF's to
>> determine logical EOT :-)).
>
> I repeat what I said in other mail- can you actually show me a tape drive
> where what I propose really doesn't work?
I think this question is the wrong way round.
Greg
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