Full disk backup size is 2x what Finder says I have *in total*...why?

Question

So, I admit it, I'm a Unix guy - it's one of the reasons OS X appealed to me in the first place. When I went to test my new external 320gb FireWire drive, I thought I'd make a full backup of my MacBookPro (10.4.11) using the tool I know best....tar. I mounted the drive and then did the backup from the command line:
cd /
sudo tar cvjf /Volumes/BigPartition/Save_All.tbz .
Hey, not pretty, but it worked. Except the backup tar file was 15GB - which was really odd since it's being compressed with Bzip and Finder says I'm using only 14GB _in total_ on my disk, and I'd expect a compressed backup to be much smaller - maybe 7GB. So it was 2x bigger than I thought it would be.
So I did it again, but this time without compression in case that was the problem (compressing already compressed data, etc). And it took up 31GB. So I'm REALLY confused here:
1) Am I using a whole lot more (17GB more!) disk than the Finder claims I am? OR
2) Is my 'tar' command saving files that don't really exist (like copies of virtual memory, etc.) that make it save 2x-3x as the actual data size would save as? OR
3) Is there some other explanation I'm not getting on this?
If #2, what's a tar command I could use to save the "real" system and data, but nothing else? Meaning, which directories/files do I need to exclude to save just the system and data I need to do a full restore, but no more?
Finally, besides the Backup app included with the OS, is there another tool/script I should be using to do a full system backup to my external drive?
thanks....and please scale the technical level of your answer to someone who programs in assembly language for fun. :}

Answer 1

You definitely need a backup program with a GUI for MacOSX. That's because of the bad news: MacOSX is not Unix. Open Darwin! Right...Apple, to my knowledge, never modified tar, cpio, dump, pax, ..., everything but 'ditto' for its augmented file system, with aliases, meta-data, 16-bit unicode fonts, resource forks, &c. All but 'ditto' will backup only Unix data in Unix files.
'Ditto' will archive HFS+ files, and can even strip architectures not needed from 'fat binaries', and use the BOM (bill of materials) to copy applications. What it does with aliases is unknown to me, but I believe it follows both soft & hard links to their sources (as tar does, I think), overwriting these if you try and restore from it. So, 'ditto' was clearly touched-up by Apple solely for creating archives, not backups.
I should examine the standard archives, like VersionTracker, for freeware from 'sourceforge'. I've never found an adequate backup applications; but I stopped looking some time ago. I just drag from Finder windows to archive, burning DVDs with 'Disk Utility'. That should work.
Note something really cute, however: a genuine tape backup released some years ago. The little mini-cartridges that fit in a digital VCR hold 20 to 30 GB! This little application was a real 'tar', sells for about $40, writes files twice, has various levels of compression, can follow aliases & links or not, and can be found on VersionTracker. After experience with quarter-inch cartridges, which were a nightmare, I distrust any tape drive that sells for less than $3000. But I've never had a VCR not playback! It's worth a look; and, what the ****, it's romantic.
Bruce
Demand Paging Forever