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Differential Backups getting larger....

Created: 10 Aug 2005 • Updated: 22 May 2010 | 10 comments

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Hello,

I am currently running Backup Exec 10 for Windows with a Full/Differential backup scheme. About 3 months ago, my differential backups we about 2GB or less, now they are running close to 6GB and no more information is being accessed than before. Correct me if I'm wrong, but I thought that the Full backup would reset the archive bit, and then the differential backups would backup everything that has been changed since the last full backup. If this is the case, I would expect the last differential backup to be larger than the first, but after the Full backup again, shouldn't the differential backup shrink to a comparable size of when it first started?

Do I have this setup incorrectly? I have this scheme setup as 2 different jobs, Differential and Full. Any help would greatly be appreciated.

Thanks
Vu Nguyen

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Sharvari Deshmukh's picture

Hello,

We would like to know whether you are using the same selection list for the full and differentail backups?

Also which backup method do you select is it diiferentail -modified time?

Thanks,

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Vu Nguyen 2's picture

Hello,

Yes the files selected in both the Full and Differential backups are identical. I am currently using "Differential-Backup changed files since last Full-Using archive bit(does not reset archive bit)". Should I change it to the mentions modified time setting for differential backups?

Thanks again
Vu

ray littlefield 2's picture

Vu- you are right with your assumption. The first differential following a Full backup should be relatively small and grow until the next full then should become smaller once again.

Check the job properties of the Full Backup job. Is the backup method 'Full-Backup Files Using Archive Bit- Reset Archive Bit' ?

Can you check the clients file system in question? There should be no files with the Archive attribute set ("A") that has a modified date older than the date of the last full backup.

Vu Nguyen 2's picture

Hi Ray,

Thank you for your suggestion. I tried and found that all the files being backed up did not have an 'A' set with a date before my last full backup. The full backup job is set to Reset the Archive bit once completed.

On a totally different train of thought, what exactly is the page file named and where is it located? Could that possibly be the reason why my backups are continuously growing?

Backups are now at 29gb/6gb (Full/Differential) and when I started a little over a month ago, it was at 24gb/2.4gb.

Ashutosh Tamhankar's picture

Here's some trivia on pagefile:

When your computer is running low on RAM, and you must have more RAM immediately, Windows uses hard disk space to simulate RAM. This is known as virtual memory. It is also known as the paging file. This is similar to the UNIX swapfile. By default, the virtual memory paging file (named pagefile.sys) that is created during installation is 1.5 times the RAM on your computer.

You can optimize virtual memory use by dividing the space between multiple drives and by removing space from slow or heavily accessed drives. To best optimize your virtual memory space, divide it among as many physical hard drives as possible. When you select drives, follow these guidelines:
•Try to avoid having a paging file on the same drive as the system files.
•Avoid putting a paging file on a fault-tolerant drive such as a mirrored volume or a RAID-5 volume. Paging files do not require fault-tolerance, and some fault-tolerant computers experience slow data writes because they write data to multiple locations.
•Do not put multiple paging files on different partitions on the same physical disk drive.

For more info:
http://support.microsoft.com/default.aspx?scid=kb;...


Regards,
Ashutosh

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ray littlefield 2's picture

The Pagefile is part of a 'hard exclusion' list, and does not get backed up; so this is not the reason for your growth in differentials.

It sounds like your setup is correct, and the only logical explanation is that the files used most often are growing.

Your observations would be perfectly normal for a home directory server that contains all the users Outlook Personal Folders files (*.PST) for example. Everytime the users login, the archive bit of these files is set- and during the day they grow. So, even the first differential backup after the Full backup would be large, and exhibit modest growth throughout the week.

If you wanted to really do heavy analysis, I would suggest increasing the logging level of the job log to list the files that are getting backed up with each differential to track what files are getting backed up. You can do this by going to Tools > Options -> Job Logs -> increase the logging level to include directories and file names.

Vu Nguyen 2's picture

Hi Ray,

Thank you for the tip on the logging. I will definately try that and see what exactly is being backed up. I post an update as soon as possible. Just got back from a conference, so I have a backlog of work to do before tackling this issue.

Cheers
Vu

Sharvari Deshmukh's picture

Hello,

Thanks for the update.We request you to keep us updated.

Regards,

NOTE : If we do not receive your reply within two business days, this post would be marked assumed answered and would be moved to answered questions pool.

Vu Nguyen 2's picture

Hi All,

Well, I said I'd give an update and here it is. The very next back that ran after I setup to log everything, the backup size shrank back down to around 2gb, which is about the normal size. I guess it was some users accessing alot of files during that time. Thanks for all the help.

Cheers
Vu

Sharvari Deshmukh's picture

Hello,

It seems that your problem is resolved please update us so that we can archive this post.


Thanks,

NOTE : If we do not receive your reply within two business days, this post would be marked assumed answered and would be moved to answered questions pool.