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Backups and Archieve Bits

Posted on 2009-05-14
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Last Modified: 2012-05-07
I back a server with 2 different software packages.
One is an online backup that does incremental backups.
The other is a local MS Windows Backup. (Windows Server 2003)
Becuase I am doing incremental backup, do any of the archive bits get reset with the MS backup and therefore confuse which files need to be backed up incrementally the next day?
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Question by:itinside
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by:btrivett
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Incremental backups always reset the archive bit.  If you don't want to reset the archive bit (i.e. you want to back up all files that have been modified since the last FULL backup), try using a differential backup instead.
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by:itinside
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Does the MS backup interfere with the Incremental backup?
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by:btrivett
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Well, basically, when you use an incremental backup, the backup utility will turn the archive bit off, which indicates to your operating system that the file has been backed up.  If you use another backup utility that also utilizes the archive bit when it performs backups, it will view that file  as already having been backed up and it will, in turn, skip over that file.

For that reason, it's really not great to use two backup utilities that both perform incremental backups.  If you have the space on your backup media, you may want to perform differential backups instead of incremental.
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by:btrivett
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I apologize.  I don't think I realized before what you were actually asking.   think I may understand your confusion now.  When you create a backup using MS Backup, I believe the default backup type is "Normal" which also resets the archive bit (similar to what an incremental backup does).  When creating the backup in MS Backup, you can click the "Advanced..." button at the end of the wizard to change the backup type to "copy", which will basically just copy the files you select without modifying the archive bit.
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by:SelfGovern
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btrivett is mostly right... Just understand that you can't use two different backup applications interleaved without being very likely to run in to problems -- unless all you do are full backups.

Full backup: Backs up all files, resets archive bit.
Incremental backup: Backs up only files with archive bit set, resets archive bit.
Differential backup: Backs up only files with archive bit set, does NOT reset archive bit, so that the same files (plus new changed files) will be backed up next time again.

Decent backup programs will allow you to back up according to whatever scheme you need, then copy backups from one place to another -- might this be easier?

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btrivett earned 500 total points
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I think the confusion, though, may have a good bit to do with the terminology used in MS Backup.  In that particular application, a "Full" backup is actually called a "Normal" backup, which is the default backup type.  These are the options you have with MS Backup:

Normal:  Backs up all selected files, and marks each file as backed up (by resetting the archive bit)
Copy: Backs up all selected files, but does not marks any file as backed up (does NOT reset archive bit)
Incremental: Backs up selected files only if they were created or modified since the previous backup, and marks each file as backed up (resets archive bit).
Differential: Backs up selected files only if they were created or modified since the previous backup, but does not mark them as backed up (does NOT reset archive bit)
Daily: Backs up only the files that were created or modified today.

If you create a backup using MS Backup's wizard, without modifying their "advanced" settings, though, you never see these options.  All of your backups will be "Normal" backups... which means that every backup will reset the archive bit.  That being the case, let's paint a scenario for you:

Weekend: You create a "Full" backup with the offline solution and/or "Normal" backup with MS.  The archive bit for every file that you've backed up is now turned OFF indicating the files have been backed up.
Monday: Your users modify and/or add 100 files or folders to a directory that is a part of your backup routine.  The OS turns ON the archive bit for all of those files to indicate that those files have not been backed up.
Monday night: You run an incremental backup using your offline backup utility.  Only those 100 files/folders get backed up AND the backup utility turns the archive bit back OFF for those files to indicate that they have been backed up. Life is good...

But now the fun begins...

Let's say that on Tuesday, your users add/modify 200 files/folders.  All archive bits for all 200 of those files are now turned ON.  Typically, those 200 files would be recognized and backed up by your offline incremental backup... but now there's a twist:
Tuesday night at 8:00 P.M.: You run a "Normal" (the default setting) MS Backup on the same directory that your offline backup utility backs up.  That backup runs until 11:00.  As MS Backup backs up EVERY single file/folder in that directory, including the 200 files added/modified that same day, it resets (turns OFF) the archive bit for EVERY single file in that directory.

So...
Tuesday night at 11:30: You run your offline incremental backup, which looks for files and folders that have been modified since your last backup.  But, guess what?  Your last backup just completed 30 minutes ago... which means that, in all likelihood, your incremental backup will back up absolutely nothing. :-)

Obviously, your schedule may be different, but hopefully you get the idea.  If you run the MS Backup at any point in time between your offline incremental backups, your incremental backups WILL NOT capture all of the files that were modified since the last incremental backup.

So, if you don't want to invest in a more robust backup solution, and you want MS Backup to back up ALL of your files without interfering with your offline backup routine, change your MS Backup type from "Normal" to "Copy" and leave the "Full" and "Incremental" backups to your offline utility.

Clear as mud, right? I hope that helps... :-)
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by:itinside
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BTirvett thank you for following through so well.

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