compressing a tar file
 

I have a tar file that is 11.5 GB large. I want to copy it to a DVD disk. Therefore at present it is too large. It is a tar file created with the command;:

tar -cf works Desktop

which put all of the files on the desktop (plus subdirectories). Now I do not think it is compressed, so can I use a command to now compress this tar file? if so what is the command.

I could start over creating gzipped tar files from scratch, but these tar files have been checked and approved by our network so that would make it a much longer process, if I went through thta again.

Any help appreciated. Thanks in advance.


Respectfully,


jyunker

Let us know where you get stuck.

compressing a tar file followup
 

Okay, what is the difference between zip and gzip? I can use either whiih has the greater compression?

R,

jyunker

mite depend on data but i think bzip2 has the greater of compression.

If you have the time, you can use 'J' which is 'xz' that has the most compression of all.

http://pokecraft.first-world.info/wi..._vs_LZ4_vs_LZO

@jyunker:

tar jcf -> use bzip2
tar zcf -> use gzip
tar Zcf -> use zip
tar --xz cf -> use xz

Untar: tar xf

When untarring you do not have to specify the compression that is used, tar is smart enough to figure it out.

Thanks for that nugget!

The "if you have time" reference means it takes longer than say my usual "tar -pczf"?

jyunker, unlikely you are able to compress 11.5 GB to fit into DVD (unless all of that is text). In order to compress your TAR file, use "xz":

This will take a lot of time. But instead you might want to consider splitting your tar archive to fit it into three DVDs:

This will split "file.tar" into 4500Mb-parts and name them "file.tar.aa", "file.tar.ab", "file.tar.ac" and so on... Don't forget about period in the very end of the command (it will make extension visible for you). Then, in order to assemble files into source one, `cat` them like this:

How much you can compress that tar-archive is dependent on its content. If it is mostly text then you will get very good compression rates. If it is images or videos you will likely end with a larger file after compression, since those files usually are already compressed and compressing them again does nothing but adding overhead. But as Mr. Alex already pointed out, splitting the file may be the better option. Also, keep in mind that you can control the level of compression, a xz -9 will use better compression techniques, but will be significantly slower, while a xz -1 will go faster, but result in a larger file.

By the way, there is a new super fast compression algorithm: http://code.google.com/p/lz4/ .