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NTBackup Questions

Posted on 2004-09-19
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Ok, I've got an NTBackup scheduled that is set to incremental and replace the existing backup. This backup is run every day. It is my understanding that with it set up this way only the things that have changed from the previous day will be written to the tape drive, and that they will overwrite the previous version of the files that have changed. Is this correct? It's about 5 GB of stuff, and I want it to be backed up like this so that the tape will slowly fill up rather than filling up in a matter of days.

Also, I was wondering if there was a way to find out how much free space was left on the tape without having any third party software. We are using W2k3. Thanks for your help.
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Question by:Grime121
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by:Quetzal
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Your setup will do as you want it to, changed files will overwrite previous backup set.  Remember, backup determines what files have changed by checking the archive bit (which gets set whenever a file is changed and cleared when the backup is done).  So on day 1, a backup set is written with the files that were changed that day.  On day 2, a new backup set is written with the files that were changed that day.  As of day 2, the only backup set written on the tape will be from day 2.  Any files that changed on day 1 but not on day 2 will not be on the tape.  This may not be the behavior you are seeking.

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by:Quetzal
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NTbackup does not do compression.  Therefore if you have a 10/20 GB tape, you can fit about 10GB (unless your tape drive does hardware compression).

I think that you may want to rethink your tape rotation.  I like to size the drive so that a full backup fits on one tape, then depending on your needs and the amount of data that changes daily, configure daily backups so that I can see any changed files during the week (which your current scheme does not do).

if the total amount of data is 5GB, then generally only a small portion will change each day.  Let's say you have a 10/20 GB tape drive and 1-2 GB changes daily and that you do a full backup (on a separate tape) on Fri.  Then on Mon do an incremental-overwrite to initialize the daily tape with the files that changed since the full backup.  Then on Tue-Thu do an increment-append to add the files that changed on each day to the tape.  At 1-2 GB changed per day, you can easily fit all the changed files for Mon-Thu on 1 tape.

But now let's say the your have a 10/20 tape and 5 GB changes daily.  Then get a tape for each day and do an incremental-overwrite.  This way the set of daily tapes will contain all the changed files for that week.  In this example, with 5 GB changing daily, you can't guarantee that more than 1 day will fit on a single tape.
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by:Grime121
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What about finding out how much free space is left on the tape? What's the easiest way to do that?
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by:nobus
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Why not use a Rev drive? portable, easy to use and much faster  !   Look here :

http://www.iomega.com/na/products/family-save.jsp?FOLDER%3C%3Efolder_id=16006169&ASSORTMENT%3C%3East_id=63191
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by:Cyber-Dude
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OK
Incremental backup actually clears the archive bits after each backup thus allowing you to backup only newely added or modified files. The modified files are override the already existing files on the tape and the newely added files are just added. If you remove files from any backup destined location; the file it-self wont be deleted from the tape if previously backed up.

In my opinion, if your capacity is rather small; you can initiate a full backup each day, overriding the backup on previous day. If you want to be really sure of your backups and data is rather important to you, purchase five or six tapes (each for each businss day) and commit a full differencial backup (i.e. the archive bit is not deleted from each file) on each and every business day while taking the previous day backed up tape to a safe place (i.e. Home). Each full backup will override the previous backup made thus allowing  you to achieve the following advantages:
1. Easy to restore option (the same as today).
2. If your backup capacity stays arround the 5GB, it will provide you with propper space estimation (just remember what Quetzal said about 10/20GB tapes)..
3. You will have a backup available in-case a disaster occures on the location where the data is...

Hope that helped

Cyber
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by:Quetzal
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There is no exact way to know how much space left on a tape.  You can approximate by figuring out how much has been written to the tape.
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by:Grime121
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Ok, how can I find out how much has been written to the tape?
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by:Cyber-Dude
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You may verify it using NTBackup Report...

Cyber
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Quetzal earned 300 total points
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Cyber's got it...run ntbackup go to Tools->Report.  You should be checking this report after every backup in order to make sure the backups are running correctly.
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