Incremental backups are big

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Re: Incremental backups are big

Veeam Logoby Shestakov » Wed Apr 08, 2015 10:07 am

Thanks Dmitriy,
But the question was about full backup size. Is the size of full backups same for those VMs?
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Re: Incremental backups are big

Veeam Logoby centneroff » Thu Apr 09, 2015 12:12 pm

Yes, the full backups sizes are almost the same. 1,49TB and 1,47TB.
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Re: Incremental backups are big

Veeam Logoby Shestakov » Thu Apr 09, 2015 5:33 pm

Thanks for the reply,
The significant difference between incremental backup sizes can be caused by a number of reasons: Above-mentioned Deduplication, Antivirus, Defragmentation, Exchange, SQL or just blocks of the 1st VM chane more intensively than of 2nd because of inner applications activity.
Let`s see how that will change after you shut down antivirus scanning and make active full backup.
Thanks!
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[MERGED] One VM With Consistently large VIB's

Veeam Logoby ThaVWMan » Wed Nov 09, 2016 8:19 pm

I have one VM that I cannot seem to nail down what is causing huge amounts of changed blocks on a daily basis. The guest is running 2008 R2, and is also a domain controller. It has to virtual disks, and the c: disk is the one that has around 24GB of changes backed up each job run. There are no file shares off of this drive aside the ones for AD. Here is what I have done to narrow down the issue thus far.

1. Turned off AV, no change.
2. Verified there are no scheduled tasks running.
3. Moved print spool folder to different drive (grasping at straws here).
4. Starting running backup job twice daily, would have thought my vib files would have been about half the size, but they stayed consistent.
5. Windows reports drive is about 50% fragmented. I have gone through other threads on here, and it seems to be that this could be a source but also may not matter. Some things say that this causes small file changes to create large amounts of changed blocks, others say to not worry about defragging a disk any more.

I have not tried turning off CBT, as I can guess it would make the files much smaller, it is not really a valid solution. I have other servers that i back up such as exchange, database servers, and other domain controllers that do not have any where near the size of changed blocks that this one does. I am at a loss of what else to look at on this system. Any ideas would be great!
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Re: Incremental backups are big

Veeam Logoby Shestakov » Wed Nov 09, 2016 9:28 pm

Hello Nick and welcome to the community!
Indeed small change causes the whole data block to be copied. Antivirus is only one of the possible reasons.
Please read the thread above and check if you have the same issue.
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Re: Incremental backups are big

Veeam Logoby ThaVWMan » Wed Nov 09, 2016 9:41 pm

I believe I did find this thread as well before posting, but still have not been able to nail down what is causing the changes. I have not found any of the items in this current thread to be the culprit for the large backup files thus far. As far as I can tell, this disk should only have minor changes daily caused by regular AD activity. There are no other apps running on this system, and the file shares are on a different disk. The C: drive contains windows system files and the AD sysvol, that is it as far as I can tell. No other drive in my environment has any where near this level of changed blocks on a daily basis, including my SQL and Exchange systems. I dont get it, and this is becoming a huge issue as it is making daily offsite replication difficult. Can CBT be turned off for just one VM, or even just one disk in a VM, within a job that has other VM's in it? Or would I have to create a special non-cbt job just for this one system?
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Re: Incremental backups are big

Veeam Logoby v.Eremin » Thu Nov 10, 2016 9:43 am

If you turn off CBT, our own proprietary mechanism will be used to determine changed blocks. Most likely, it will find the same amount of changed data, and increment similar in size will be created.

You can try to reset CBT, if you think it misbehaves. Otherwise, open a ticket with out support team. Through deeper investigation the root cause will be found.

Thanks.
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Re: Incremental backups are big

Veeam Logoby ThaVWMan » Thu Nov 10, 2016 1:13 pm

How do you reset CBT, and by doing that, it will cause a full backup to be taken, correct?
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Re: Incremental backups are big

Veeam Logoby Shestakov » Thu Nov 10, 2016 1:58 pm

Nick CBT reset instruction is here. It will not cause full backup, but the increment size will equal a size of full backup. You can perform full backup manually if you wish.
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Re: Incremental backups are big

Veeam Logoby Vsevolod Zubarev » Mon Nov 14, 2016 7:48 am

Resetting CBT isn't going to help since identical blocks are still to be filtered out by our own deduplication.

Common reasons for large incrementals:
- Windows Deduplication (not applicable in your case since it's a system volume)
- Periodically scheduled in-guest shadow copies.
- Potentially any other scheduled activities that you might've set up.
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Re: Incremental backups are big

Veeam Logoby Matts N » Thu Nov 17, 2016 2:41 pm

Hello ThaVMMan,
A quick and maybe stupid question: is it possible that you by accident have enabled backing up the swap file? Normally this is excluded, but it could explain the large changes on disk.

// Matts
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