tar file size limit and tar to tape

tar file size limit and tar to tape

Post by Pui Ming WO » Sat, 09 Jan 1999 04:00:00

Someone told me that using tar to backup a set of files/directiores
to one tar file have a limit that the latter will not exceed 2Gb
Now does this limit apply also when i tar to a tape
i.e. e.g. tar cvf /dev/rmt0 .


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1. Wanted: rcmd host tar x_?_vqf file.tar file1 ... fileN | tar xvf -

[X-posted to c.u.sco.misc & c.sys.sun.misc, no Followup-To set, I'll
check'em both]


SCO v4.2 box as digital voice recorder, archiving VOX-files to Network
Jukebox Controller (basically HP MO Jukebox with 16 slots) running SunOS
4.1.3 sparc (sun4c). NJC is used for general backup/archive for whole
network. Size
of each archive tar-file is 300 MB, containing about 2500 VOX-files. So
far so good. But when it comes to user requesting old calls to be
replayed, he/she must wait a bit. At the moment, the restoring process
(say, of 100 VOX-files) is done with the following:

rcmd NJC cat archiveN.tar | tar xvqf - ${files_to_restore}

which is CPU time and network bandwidth wasting, if the files are not
stored at the beginning of archive ('tar ..q' - quits immediately when
all files are extracted). On average, the NJC must read 150 MB from MO or
cache and send it to the SCO box over network, even if only one file/call
is requested. Network and SCO box are very busy, so it may even take about
half an hour. It isn't really bad (users seldom complain about it), but it
could be much faster.

I'm about to work around it with something like this:

rcmd NJC "(
  taroffs archive.tar ${files_to_extract} | while read offset nbytes
    dd < archive.tar iseek=$((offset/512)) count=$((nbytes/512))
    # OK, If SunOS 4.1.3's 'dd' does not support
    # 'iseek' or smthg like that, I will use my tool:
    # fildes archive.tar,${offset} : dd count=$((nbytes/512))
)" | tar xvf -

Yes, this needs utility `taroffs`, which would print out offsets and sizes
for the specified files in the given archive. No problem, but:

The question is:

before I will code it (`taroffs`), I'd like to know, whether anyone knows
of some tar-like app, which has the option, which is missing in the
${subject}. Instead of restoring the files to disk, it should extract the
files to std. output as a smaller tar-archive. Note that it must support
also the 'q' option mentioned above and of course it must be able to
*lseek()* (in the archive) over files (not *read()* them), which are not
of interest. Otherwise, such option would be useless in this situation.

I'm looking either for SunOS 4.1.3 sparc binary or sources, which I would
able to compile on SunOS 4.1.3 (sun4c) or 5.[34] (sun4m/sparc).

Any other solution ?
No, NFS isn't part of SCO v4.2 Open Desktop Lite 3.0.0.

Thanks for reading this far and for your time.

Radek Tomis

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