dd to and from tape; using diff to compare
See dd also.
From: Tony Lawrence <email@example.com>
Subject: Re: Edge backup with Seagate Travan tape.
Date: Tue, 19 Nov 2002 12:08:20 -0500
> Here's the correct version:
> # dd if=/etc/termcap of=/dev/rStp0
> 288+1 records in
> 288+1 records out
> # dd if=/dev/rStp+ of=/termcapcopy
> dd: cannot open /dev/rStp+: No such file or directory (error 2)
> # dd if=/dev/rStp0 of=termcapcopy
> 289+0 records in
> 289+0 records out
> # diff /etc/termcap termcapcopy
> Warning: missing newline at end of file termcapcopy
> something wrong here... does this tells you anything?
It tells me you don't understand dd :-)
If you want to test something like that, do it like this:
cp /etc/termcap /tmp/this
tar cvf /dev/rStp0 /tmp/this
tar xvf /dev/rStp0
diff /tmp/this /etc/termcap
The problem with using dd for this is the differing blocks- notice you
get 288 full blocks plus a PARTIAL block going out to the tape, but the
tape can only give you full blocks back. - therefore there is null data
in the read, and that naturally won't pass diff.
> "Bill Vermillion" <firstname.lastname@example.orgREMOVE> wrote in message
>>In article <email@example.com>,
>>Ulven <freddy@REMOVESPAMulven.com> wrote:
>>>Here's the resault:
>>># dd if=/var/log/backup.txt of=/dev/rStp0
>>>1+0 records in
>>>1+0 records out
>>Who knows how bitg backup.txt is. I just suggested /etc/termcap
>>as it is decent size.
>>The concept is to use dd to put a file to tape. 'if' is the name of
>>the input file and in this case 'of' is the name of the tape.
>>The we reverse this and use 'if' for the tape devcie and 'of' for
>>the name of the file we will create as data is taken from the tape.
>>Then we compare, using diff, to see if the contents of the file
>>we put on tape match what we just took off the tape.
>>># dd if=/dev/rStp0 of=/var/log/temp
>>># diff /etc/termcap termcapcopy
>>>diff: cannot stat termcapcopy: No such file or directory (error 2)
>>You have to diff the files you put to tape and take from tape.
>>I said eg dd if=/etc/termcap eg meaning 'for example. It's a
>>standard reference but perhaps I should have said e.g. - but
>>everyone seem to skip that now.
>>Bill Vermillion - bv @ wjv . com
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