[TUHS] Ultrix Tape: Block Size?

[Warner Losh]

I'm glad you corrected because when they worked, they were awesome. When
they didn't, life had a lot of swearing in it... And when I was sysadmin
for the MicroVAX II that had them, I swore like a sailor....

Warner

On Mon, Oct 15, 2018 at 3:04 PM Clem Cole <clemc at ccc.com> wrote:

> #$%^ - they >>weren't<< like DECtape from a reliability standpoint ...
> ᐧ
>
> On Mon, Oct 15, 2018 at 5:00 PM Clem Cole <clemc at ccc.com> wrote:
>
>> Be careful, TK-50 is different than 9-track.  It's a streamer tape like
>> QIC, 4mm and 8mm.   The blocking is done under the covers by the HW and the
>> blovk size if just how a DMA is done.  I recommend that you pre-fetch the
>> read with dd or double-dd setting ibs=64k, obs=20b and conv=sync and pipe
>> the output to the reader (tar/cpio or the like) [if that fails try
>> obs=1b].   This should work well as can (TK-50 overall suck - don't set
>> your hopes high on anything with them -- they were DECtape from a
>> realiabilty standpoint, they were different from the reset of the world,
>> the performance was poor and they were expensive).
>>
>> Anyway, by using dd or the like a front end, it will allow the read
>> streamer to read as fast as it can.  The problem is that the way it works
>> under the cover does not shine with traditional UNIX I/O.  BTW: ibs of
>> anything more than 64K on a VAX (or PDP-11) will not help because of the
>> dma size on the Unibus caps DMA read/writes at 64K.   On a PMAX or (under
>> Tru64 on a Alpha), you can try using really large ibs sizes depending on
>> your physical memory size.
>>
>> BTW: What will help the most is actually finding a copy of the old
>> double-dd program (from the UUNET archives) which forks off two child
>> procees to perform the actual I/O and alternates between the two processes
>> via pipe between them and controller - so one dd process is reading when
>> the other dd process is writing.  [It used to be called: ddd before the
>> Gnu guys grabbed that name for the debugger].   The command line might be
>> something like:   ddd ibs=64k obs=20b | tar xvpf -
>>
>> FWIW:  I wrote a version of a fast dd years ago that used pthreads and a
>> semaphore that I should still have kicking around.   At one point when I
>> was dealing with streamer tapes for backup, I definitely ran it on Tru64
>> and FreeBSD, but  I've forgotten where Ultrix fell.
>> ᐧ
>>
>> On Mon, Oct 15, 2018 at 4:01 PM Warren Toomey <wkt at tuhs.org> wrote:
>>
>>> All, I received this request from Matthew who isn't subscribed to either
>>> the TUHS or cctalk lists. He knows how to read the lists archives. Many
>>> thanks for any help you can provide.
>>> Cheers, Warren
>>>
>>> ----- Forwarded message from Matthew Whitehead -----
>>>
>>> Date: Mon, 15 Oct 2018 08:25:39 -0400
>>> From: Matthew Whitehead
>>> Subject: Ultrix Tape Blocks
>>>
>>>    Warren,
>>>      I wonder if you can give me a referral. I want to install Ultrix-32
>>>    on my MicroVAX II using the ancient TK-50 tape drive. I know the tape
>>>    files are on your archive, but I need to know the block size for each
>>>    of the many files; it can vary a lot.
>>>    Who might be able to help me with this?
>>>    Matthew Whitehead
>>>
>>> ----- End forwarded message -----
>>>
>>