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Old 07-27-2009, 06:02 PM   #1
krishnaix
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Backups


Hi All,

I am New to linux operating system.I am facing troubles while doing backups.
What is the basic difference between Incremental and Differential Backups.
Do they require special software to perform.

Thanks a Bunch.
 
Old 07-27-2009, 07:21 PM   #2
Suncoast
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Incremental and Differential will only backup files that have been modified and have the "a" archive file attribute on.

Differential will not clear the "a" attribute, incremental will.

You should only use these types of backups when you know you have at least one good FULL backup already.

The differential and incremental backups are intended to save time and resources doing daily backups, while the full backups are typically done when there is more time and system resources, like on Sunday for businesses.

All backup software I'm aware of will do these, even tar.

Last edited by Suncoast; 07-27-2009 at 07:26 PM. Reason: Addendum
 
Old 07-27-2009, 08:40 PM   #3
choogendyk
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First off, the archive bit is typical of Windows and the NTFS file system -- http://en.wikipedia.org/wiki/Archive_bit. In many file systems, it doesn't exist; and, it has been severely deprecated, because it is not under the control of a particular backup system and can be changed in ways that mess up backups when more than one tool is used, or when a user starts messing with it. See W. Curtis Preston's article "The Windows archive bit is evil and must be stopped."

Different backup programs have their own means of tracking what needs to be backed up. Dump, such as ufsdump, tracks when filesystems were last backed up in /etc/dumpdates. Whether something gets backed up in an incremental is determined by whether it has changed since the last backup. For a fairly good description of incremental and differential backups, see How are Backup Levels Defined?. (I confess to having written the first section of that page and having edited the rest).

There are a huge variety of strategies for doing backups. A common approach is a full backup on weekends, and incrementals on week nights. Another is a full backup at the beginning of a month, a differential every weekend, and an incremental every week night. How long backups are kept also varies a lot. Since I use Amanda, my full and incremental backups are distributed across the dump cycle to even the load (see the description in the link above). I have a dump cycle of 1 week. I run backups every night, and I have a tape cycle of 6 weeks, with some extras on top of that. I also keep periodic archives.

Last edited by choogendyk; 07-27-2009 at 08:41 PM.
 
Old 07-28-2009, 09:53 AM   #4
Suncoast
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Uh-oh! I've been busted again for my Windows-centric background.

To the Original Poster Krishnaix:
Full backup = Full Backup
Differential = Backup everything since the last FULL backup
Incremental = Backup everything since the most recent (full or incremental) backup.

When not using the archive bit, the most basic way to do differential or incremental backups is by tracking and using the previous backup date.

You did not say what kind of problems you are having, or which backup program you are using. If you let us know, we'll try to help you out.


To choogendyk: When someone starts with "I am new to Linux," I try to keep it basic. I do agree with everything you said. And thank you for pointing out I was drifting back to Redmond world.
 
Old 07-28-2009, 11:12 PM   #5
krishnaix
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Thankyou very much guy's. Appreciated, it is more helpful.
 
  


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