can anyone help

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Top Forums UNIX for Advanced & Expert Users can anyone help
# 1  
Old 08-14-2001
can anyone help

I'm hoping that one of you more expert Unix users could help me with compressing and writing to DLT. The current string I am using is : tar -cvf /dev/mt/tps2d1nrnsv filename

I am writing to DLT IV tapes on a DLT 7000. The tapes hold 40GB uncompressed and 80GB compressed, but you probably already know this. Just trying to pack more on a tape.

Any help is greatly appreciated.
# 2  
Old 08-14-2001
I you want to compress the file, try creating the tar file with the -z option. As I recall, this should compress the file as the tar is created.
# 3  
Old 08-15-2001
Device file

Check which device files in /dev/rmt/ are all pointing to your DLT drive. Usually you have a device file with and without compression I/O. Also check the settings on the drive itself. You should always be able to override compression settings on the drive itself.
# 4  
Old 08-25-2001


You probably know this, but I will mention it anyway.

When you compress, in most cases, you get around 80% compression. While this will save space on your tapes, it will also slow down recovery from the tape should that be necessary.

If this is data that is being archived for long term storage, then your need to compress would be a valid one.

Just remember, the more you do to the data to get it onto the tape, the longer it will take you to get it off of the tape later.

Also, you may want to look at "gzip" as well. It may get better compression than "compress", if I remember correctly.

# 5  
Old 08-26-2001
Check your tape system documentation.
The "compression" they refer to is
device level compression and even though
they may say 40/80GB, you can typically
expect an average of a 1 to 1.5 compression
ratio (60GB) after all is said and done.
There are many binary files which will not
compress well at all (in some cases they
actually increase in size). You can (as previously
suggested) use software compression such as
"compress" or "gzip" to be able to get more
data on the tape but if you do so, the
device level compression (if used) may end up
increasing the size of the data stored to tape.
# 6  
Old 09-19-2001
just my five cents
what about
tar cvhf /dev/mt/tps2d1nrnsv .
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