From owner-freebsd-hackers@FreeBSD.ORG  Thu May 16 23:56:15 2013
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Date: Thu, 16 May 2013 19:56:14 -0400
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Subject: Re: tape (sa0) on sparc64 ?
From: Zaphod Beeblebrox <zbeeble@gmail.com>
To: Bob Bishop <rb@gid.co.uk>
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On Thu, May 16, 2013 at 5:08 PM, Bob Bishop <rb@gid.co.uk> wrote:

> Hi,
>
> On 16 May 2013, at 21:51, Zaphod Beeblebrox wrote:
>
> > I have to retrieve some very old backups.  They were made on FreeBSD and
> > are on tape... specifically DDS4.  [etc]
> > However, attached to either controller (after a reboot of the machine
> and a
> > powercycle of the drive), I get:
> >
> > [1:25:325]root@run:/home/foo> dd if=/dev/sa0  of=tape5
> > dd: /dev/sa0: Input/output error
> > 0+0 records in
> > 0+0 records out
> > 0 bytes transferred in 0.002930 secs (0 bytes/sec)
> >
> > ... which is a return code of '1' and no messages on the console...
> >
> > I have, before you ask, tried "bs=10k" and 20k ... but I believe this
> > command should run by itself fetching the first 512 bytes of each block
> ---
> > narrowing down the block size logically comes after making the tape go.
>
>
> Try bs=64k
>

Same result.  Besides, as far as I understand, the proper operation (if the
blocksize is too small) is to read the first $n bytes and then write them
to the output..

But same result.