The following was from a post on a Linux forum back in 2008. Modern versions of tar should be able to handle large file sizes. The other points would also be valid. It's possible that the way tar is compiled it's lacking large file support, but that shouldn't be the case. BusyBox fixed this back in 2006
Three things that effect file size limitations are the 1. the kernel, 2. the file system and 3. the application. Since Debian Etch uses a 2.6 kernel I would rule out 1. unless you have compiled your own kernel and did not include large file support. 2. Would only be a problem if you are trying to save the file to a FAT32 file system or using a kernel that did not include large file support and 3. would be a problem if using an old version of tar which does not handle large files.
So what kernel are you running, what file system are you trying to save the tar file on and what version of tar are you actually using? Doing some googling there appeared to be single file size limitation of 2GB but again I believe the latest version can handle a single file of 68 GB.
To see if your version of tar has large file support: strings `which tar`|grep 64
If you are trying to save to a network share then you could have samba limitations depending on version.
So basically it is difficult to say what the problem is without additional information.
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