From: Jean.Desrosiers@VISAER.com
Date: Tue May 04 2004 - 07:55:53 EDT
Many thanks to those who took time to respond.
The lesson here is to not discount the obvious "too simple to work" answer.
THE QUERY....
===========================================================================
Is it possible to create a tar tape from a compressed tar archive file, blah.tar.Z, without the need to extract and write the contents of the compressed archive to disk first? I need to duplicate a tape that I made months ago and disk space is an issue. Besides it's so inefficient.....
I've tried a couple of combinations zcat'ing the archive and end up with the files being written to the directory I am in and nothing going to tape.
I firmly believe that someone out there has the elusive one line command that will do it. Maybe something combined with dd?
THE ANSWERS...
( From Eef Hartman, the answer I put to use. J )
You don't want to put the COMPRESSED image onto the tape?
If not:
zcat filename.tar.Z | dd of=/dev/rmt/0m obs=<blocksize> should put the tarfile onto tape (fill in your own tape device and blocksize), while just pure
dd if=filename.tar.Z of=/dev/rmt/0m bs=<blocksize>
will put it COMPRESSED onto the tape (you might want to use the non-hardware compression tape device for this, if you got one, like:
crw-r--r-- 2 bin bin 205 0x003000 Jun 4 2001 0hc
crw-r--r-- 2 bin bin 205 0x003080 Dec 20 2002 0hcb
crw-r--r-- 2 bin bin 205 0x003040 Dec 19 16:09 0hcn
crw-r--r-- 2 bin bin 205 0x0030c0 Jun 4 2001 0hcnb
crw-r--r-- 2 bin bin 205 0x003001 May 1 16:26 0m
crw-r--r-- 2 bin bin 205 0x003081 Nov 20 2002 0mb
crw-r--r-- 2 bin bin 205 0x003041 Sep 2 2002 0mn
crw-r--r-- 2 bin bin 205 0x0030c1 Nov 3 2001 0mnb
crw-r--r-- 2 bin bin 205 0x003000 Jun 4 2001 c0t3d0BEST
crw-r--r-- 2 bin bin 205 0x003080 Dec 20 2002 c0t3d0BESTb
crw-r--r-- 2 bin bin 205 0x003040 Dec 19 16:09 c0t3d0BESTn
crw-r--r-- 2 bin bin 205 0x0030c0 Jun 4 2001 c0t3d0BESTnb
(the "BEST" ones are automatic generated, with BEST compression, the 0hc* ones are links TO those, while the 0m* ones are with compression DISABLED, this is for a DDS tape drive on SCSI bus 0, address 3 on a 735). As you can see the bit with value 1 disables compression here (minor).
Note that the 0* ones have been generated by ME, are not the default ones.
Try this:
zcat blah.tar.Z > /dev/rmt/0m
( It works but when tabling the resultant tape tar complains about reaching the end of tape and requires user input to continue. J )
The slightly fancier version, functionally equivalent unless your tape drive is very picky about blocking factor:
zcat blah.tar.Z | dd of=/dev/rmt/0m bs=10240 ( Same as first best working answer J)
The block size of 10240 emulates the default blocking factor of "tar".
haven't you tried the 'obvious' ? :
(there's that obvious thing I foolishly discounted in favor of a more complex solution. J )
uncompress < blah.tar.Z | dd of=YOUR_TAPE_DEVICE obs=10k
(or : zcat blah.tar.Z | dd of=YOUR_TAPE_DEVICE obs=10k )
10k is the (age old) 'tar' block-size ...
hope this helps,
If the origional is on tape and the target is an other tape and you have 2
tapedrives, you can do it on the fly. There are 2 basic unix 'trics' involved:
pipelining and the fact that everything can be handled as a file...
dd if=/dev/source-tape of=/dev/target-tape
Or from your blah.tar.Z file:
dd if=blah.tar.Z of=/dev/target-tape
If the source is compressed and you don't want that on the target, just
uncopmress on the fly.
zcat /dev/source-tape | dd of=/dev/target-tape
Or from your blah.tar.Z file:
zcat blah.tar.Z | dd of=/dev/target-tape ( once again, the elegant solution...J )
J Desrosiers
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