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1 Full Backup then only Differential Backups

Created: 30 Jan 2014 | 8 comments

Hello, I'm new to BackupExec and I'm just starting to plan my backup schedule/retention policy.  From the videos I've seen it appears that running occasional full backups with regular incremental/differential backups in between seems to be the recommended method.  My concern is that this will require, at a minimum, at least twice as much capacity on your backup server as the amount of data you want to backup.

My questions is, what would be the downside to running 1 full backup that is held forever and then only running differential backups that expire every few weeks?  It seems to me that this would save on disk space as you'll never need two full copies of the data on your backup server.  Are there major downsides to this?  My biggest concern would be that the integrity of the full backup remains.  If anything were to happen to that backup you'd be screwed.  Is this the reason an occasional full backup is recommended?  Does everyone out there have over twice as much space on their backup server as the size of the data they're backing up?  

I came from Retrospect which had a feature similar to this.  One full backup was done and from then on only differential backups were made.  Retrospect would then groom the backup set to remove differential backups older than your specified retention period.  Granted, it didn't really work and constantly threw errors during the grooming process (I really hate Retrospect now) but it was an option for when you were low on backup disk space.  I guess I'm just wondering if BackupExec has something similar to this that actually works.

Thanks for your help and time.

Shawn

 

Operating Systems:

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pkh's picture

In addition to the vulnerability of losing your full backup, your differential backup will grow in size over time and eventually it may become as big as the full backup. Depending on your retention period, you definitely can have more backup data than actual data. I keep my daily full backups for a week. You do the maths

Sush...'s picture

Hello Shawn,

    I would say that you have all the answers in your post itself about the disadvantage of running just 1 Full and rest Diff/Incremental backups. So as already suggested you should have Full taken at regular intervals.

 

I would recommend you to refer to these following technotes which will give you more information and will make your decision making easy about the backup strategy.

 

http://www.symantec.com/docs/HOWTO73343 : How to choose a backup strategy

http://www.symantec.com/docs/HOWTO73342 : About backup strategies

http://www.symantec.com/docs/HOWTO74328 : About configuring Backup Exec to determine if a file has been backed up

 

The last technote also gives an example or scenario which explains in better way.

 

Regards,

-Sush...

Hope this piece of Information Helps you... and if it does then mark this response as Solution....!!!

sphigel's picture

Thank you both for your input.  I'll check out those articles.  It sounds like my proposed method would not work very well.  Let me just ask one more thing.  Suppose you had 20TB of data needing to be backed up but only had 30TB of disk backup storage.  Is there any reliable backup method that would work in this scenario?  Or is the only answer to get more backup storage?

Thanks again.

Shawn

Sush...'s picture

Hello Shawn,

    You can run Full backups on weekends with retention period of just 5 days.... and then daily Differential backups with Retention period of just 1 day.

So you Daily backups will be overwritten daily and then Full backup will be overwritten during the next full backup which means the space will be retained.

 

Regards,

-Sush...

Hope this piece of Information Helps you... and if it does then mark this response as Solution....!!!

sphigel's picture

Thanks for the reply.  It is my understanding that the first full backup would not be erased until the second full backup is completed.  If that is correct then it would not work in my scenario.  In that case you would need over 40TB of backup storage space to backup 20TB of data.  Please let me know if I'm wrong about this.  

Thanks,

Shawn

pkh's picture

Your understanding is correct. In fact, it is not only the full backup, it is the entire backup chain, I.e. the full backup and any incremental/differential backups after that. The first chain will not be groomed until the next chain is completed

In your case there is no way out, you need more storage space

Sush...'s picture

Hello Shawn,

   The information that the Full backup set can not be deleted until the second full backup is completed is not updated. That issue was pre- SP1. Now with SP1 and later service packs you will be able to groom even the last backup set.

Please check the following how it is done:

Cause #2: DLM in Backup Exec 2012 has a rule to always keep the last copy of the latest recovery point chain per job definition per resource. This rule is enabled as default to guarantee that there is always a valid data recovery point.  With this rule enabled, the backup sets that belongs to the last copy of these latest recovery point can not be groomed even when they are expired.

A recovery point chain is a chain of backup sets required to restore data to a point-in-time, for example [Full, Inc1, Inc2] is a recovery point chain that is needed to recover data to the point-in-time of Inc2. The latest recovery point chain is a chain of backup sets required to restore data to the latest backup point-in-time.

 

a. Check if many one-time only backup job have been created, and they only ran once or twice;

b. Check if there are old backup solutions that have been run before but are not scheduled to run any more.

 

To resolve this issue, the following registry value can be configured to disable the DLM rule mentioned above.

 

Note: Service Pack 1a (TECH186717) must be installed to proceed with the fix listed below. After installing SP1a, create the following registry key to turn on/off the "Keep the last and latest recovery chain" DLM rule. 

Warning: Incorrect use of the Windows registry editor may prevent the operating system from functioning properly. Great care should be taken when making changes to a Windows registry. Registry modifications should only be carried-out by persons experienced in the use of the registry editor application. It is recommended that a complete backup of the registry and workstation be made prior to making any registry changes.

1. Open Registry on the Backup Exec Media Server
2. Start->Run->Regedit
3. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Symantec\Backup Exec For Windows\Backup Exec\Server
4. Create a new DWORD value named DeleteLastRecoverySetsOnceExpired

5. Modify the value to 1

 

Please refer to this official technote to get more information on the same:

 http://www.symantec.com/docs/TECH187957 : Backup 2012: Some expired backup sets are not being deleted after the expiration date or unable to overwrite or delete the last backup set.

So with this setting it will be possible for you to take the entire weeks backup and erase / groom it during the next Full.

 

Regards,

-Sush...

Hope this piece of Information Helps you... and if it does then mark this response as Solution....!!!

pkh's picture

Once the registry entry is created, it applies to all backup sets. For an infrequently backed up server, there is a danger that the last backup set is groomed when it is still needed