[Info-vax] Backup TK50 tapes

[Johnny Billquist]

On 2013-02-24 17:43, ChrisQ wrote:
> On 02/24/13 15:35, Johnny Billquist wrote:
>
>>
>> That will totally not create anything useful for him.
>> Unix, in all it's "glory" really sucks at some things. Record-oriented
>> devices is one of those things.
>> If you use dd, you'll have a lot of digging to do later, in order to get
>> something useful out of the results.
>>
>> Johnny
>>
>
> dd is about as low level as is possible to get, so if you know the block
> size, then dd will faithfully read the tape with each block as a stream
> of bytes. afaics, there's nothing magic about a vms format tape, it's
> still just a series of blocks on tape.

dd totally fails if the blocks have different sizes, which is the case here.

And no, dd is not as low level as it gets. dd makes assumptions.

> There was an earlier posting by Glen Herrmannsfeld in this group
> some months ago on just this problem:

It's a problem that have been well known and understood for over 30 years.

>>> 2) Use 'dd' to suck the entire tape into an image file under Linux
>>> and then mount it somehow under SIMH/VMS
>>
>> dd with a large value for the bs parameter (not ibs and obs separately)
>> will preserve the block structure in a tape to tape copy, though there
>> are other programs with names like tcopy that can do that. (dd will
>> stop at a tape mark.) If the blocksize is constant and known,
>> then a dd to disk can be usable, otherwise the blocking information
>> is lost.
>>
>>> Or... do I just need to get a cheapie little Alpha with SCSI to
>>> do all of this?
>>
>> Most likely any unix machine with the appropriate drive could do it.
>> Other machines may or may not be able to do it. Most popular these
>> days is a virtual tape file, as described above, written to CD-R.
>>
>> <snipped cd stuff>
>>
>> -- glen
>
> Whatever the opinion, it's still the first thing I would try to get the
> data off tape and I do still have a TK50Z, though not used for some time...

Feel free to do that, if you want. And then you'll also have something 
useless.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
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