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Click to See Complete Forum and Search --> : Why do we use tar like a unix winzip?

davolfman
10-19-2001, 02:28 AM
OK tar stands for Tape ARchive. You look at the kind of features it has and there's all the basics for backup. I noticed the article on the front page mentioning filesystem granularity because a lot of software could only do one partition at a time. My question is: why the heck does this software exist. What are the disadvantages to using tar as a backup utility. Before I accidently nuked my LFS system in-progress tar was what I used to back it up. Why don't we just use tar, or why don't we have an improved substitute (like less is for more) so we can use it as a backup utility.
stiles
10-19-2001, 11:43 AM
TAR is actually a newer backup utility. If you know any really old school Unix admin types most will have used cpio for their backups (cpio's cool cause you use it in conjunction with the find command). The reason that tar is used so often is cause it's easy and convient to perserve a directory structure (that's why developers use it to distribute their source code so they know what the directory structure is when you go to compile it). Disadvantages to using tar as a backup program, it's pretty basic. You can't do anything like dump levels where you can backup only what has changed sence your last full or lesser level backup. Ohhh yea you can't to a bit by bit check of your tape with tar, you can with some dump programs (dump is filesystem specific).

If you want to check out dump I know that SGI's XFS comes with a dump utility. From what I understand (http://lwn.net/2001/0503/a/lt-dump.php3) ext2 dump can fail under the 2.4.x.
davolfman
10-19-2001, 04:16 PM
As far as I know tar can be used for incremental backup as well.
stiles
10-19-2001, 05:47 PM
Ok, how does it do incremental backups and are you using GNU or SysV tar? I know for sure that tar will not read into the files inodes so therefore can't tell if permissions have changed (it can perserve permissions but tell if they have changed). Does -N on GNU tar specify mtime or ctime?

Even if you can do incremental backups with tar your going to have to add the logic through a script to match dump levels.

Some of the commercial backup products can to a bit level incremental backup.