Mag Tape Duplication Problems

[Geoff Clare]

In article <351 at wpg.UUCP> russ at wpg.UUCP (russ) writes:
>
>After hearing me brag about how great unix "tools" are for doing just 
>about everything, a friend of mine asked me to duplicate a reel of 
>nine-track tape that was estimated to contain app. 60 megs of data.  
>
>Although I only have one nine track drive, I do have a cartridge streamer 
>(20 megs) so I naively assumed that I could read and write the contents of 
>the nine-track in 20 meg segments to three separate cartridge tapes and 
>then concatenate the three cartridge tapes back onto a new reel of 
>nine-track tape.  I had figured that if 'dd' couldn't handle it, a 
>simple-minded program (on the order of while getchar (putchar) would be 
>able to do the job.  
>
>I suppose I could repetitiously invoke 'dd' while keeping track of the 
>total number of blocks, but I keep wondering what will happen if we get 
>down to the end of a cartridge tape and then come across a five meg file.  
>

I thought I would knock up a shell script to do the job and mail it to
Russ, but it took longer than I expected and when I was finished I
thought "Hey, this is good stuff", so I'm going to post it in the hope
that more people may find a use for it, or at least for some of the
ideas in it.

I should first issue a warning that this is totally untested, so
apologies for any bugs in it, but I think the method should work.

So here it is:


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# shell script to copy mag tape to multiple cartridge volumes and back

BLOCKSIZE=10k		# mag tape block size required
MAGTAPE=/dev/rmt8	# name of mag tape device
CARTRIDGE=/dev/rct	# name of cartridge device
BLOCKSPERVOL=40000	# no. of 512 byte blocks to fill cartridge tape

IFS="+$IFS"	# add '+' to field seperator list to ease splitting of
		# dd block counts

# write cartridges until fewer then requested no. of blocks are transferred

blocks="$BLOCKSPERVOL"
vol=1
dd if="$MAGTAPE" ibs="$BLOCKSIZE" | while test "$blocks" -eq "$BLOCKSPERVOL"
do
	echo "insert cartridge $vol and press RETURN"
	read a </dev/tty
	a=`dd count="$BLOCKSPERVOL" of="$CARTRIDGE" 2>&1`
	echo $a
	set -- $a
	blocks=`expr $1 \+ $2`
	eval b"$vol"="$blocks"
	vol=`expr $vol \+ 1`
done

echo "insert blank mag tape to receive copy and press RETURN"
read a

# write back cartridges - no of blocks on each volume is in b$vol

outvol=1
while test "$outvol" -lt "$vol"
do
	echo >&2 "insert cartridge $outvol and press RETURN"
	read a
	eval blocks=\$b"$vol"
	echo >&2 "block count should be $blocks"
	dd count="$blocks" if="$CARTRIDGE"
	outvol=`expr $outvol \+ 1`
done | dd obs="$BLOCKSIZE" of="$MAGTAPE"

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-- 

Geoff Clare    UniSoft Limited, Saunderson House, Hayne Street, London EC1A 9HH
gwc at root.co.uk   ...!mcvax!ukc!root44!gwc   +44-1-606-7799  FAX: +44-1-726-2750