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VSS and Log Truncation

smith_jones
Level 6

Hi,

We have DAG configured in our infra. Using NBU 7.7.2 we have scheduled the snapshot backup daily incremental and weekly full. But logs are not getting purged after incremental backups. I checked and found that the backup is Cumulative type in NBU, so as per NBU documentation logs will not purge.

The backup is being done for passive copy only.

Windows event logs on one of the passive node (not all but few) - 

1. The MS Exchnage Replication Service VSS Writer has successfully prepared for an
incremental or a differential backup of database 'DAG1-DB02'. The following database is mounted,
although it will not be backed up: DAG1-DB02.

2. The replication instance for database DAG1-DB02 has started copying log files.
The first log file copied was generation 12345.

3. The replication instance for database DAG1-DB02 has copied and replayed multiple logs.

4. bpbkar32 (29160) Instance1: Log file integrity check (\\?\GLOBALROOT\DEVICE\HARDDISKVOLUMESHADOWCOPY91\DAG1-DB02.log\E01):
The database engine started a new instance (0).(Time=0 seconds)

5. Instance2: A physical consistency check has been successfully initiated. The transaction log files in '\\?\GLOBALROOT\DEVICE\HARDDISKVOLUMESHADOWCOPY91\DAG1-DB02' with a base name of
'E03' will be validate. No databases will be validated.

6. Instance3: Transaction log files in '\\?\GLOBALROOT\DEVICE\HARDDISKVOLUMESHADOWCOPY91\DAG1-DB02.log' witha base name of 'E03' have successfully validated. No errors were detected.

7. MSExchange Store Worker (24972) The surrogate backup procedure has been successfully completed by DAG1Node3.

8. The MS Exchnage Replication Service VSS Writer has successfully completed a backup of database 'DAG1-DB02'. No log files were truncated for this database because the backup was a copy backup or differential backup.

----------------------------------------------------------------------------------------------------------------------------

For the 1st event, why it is saying so - "The following database is mounted,
although it will not be backed up: DAG1-DB02." Why? What is the meaning of it? The backup is successfully happening.

For the 8th event, it is saying - "No log files were truncated for this database because the backup was a copy backup or differential backup." But as per NBU differential backup purges logs.

One more thing -  I checked on internet and what I am getting is :  What is the concept of Differential backup in NBU, the same is being said by Microsoft for Incremental backup. And what is the concept of Cumulative backup in NBU, the same is being said by Microsoft for Differential backup. Means totally reverse !!

As I know w.r.t. NBU, there are normally backups of types - 

1. Full 

2. Incremental - a) Differential Incremental   b) Cumulative Incremental

3. User backup

4. User Archive

So why is there conflict in MS and NBU concept -

MS -

1. Full backup

2. Incremental backup  - logs will be purged (in NBU cumulative will not purge logs) (what incremental is saying in MS the same is being said by NBU for Differential)

3. Differential backup - logs will not be purged (in NBU logs will be purged) (what differential is saying in MS the same is being said by NBU for Cumulative)

5 REPLIES 5

Lowell_Palecek
Level 6
Employee

It is true that the Microsoft and NetBackup terminology for incremental backups differ. I don't know the history of how the terms diverged. I note that NetBackup terminology spans multiple OS types and multiple database applications. You seem to have figured out the mapping between the nomenclatures.

Regardless of terminology, it would be a contradiction leading to possible data loss for Exchange to truncate logs after a cumulative backup.  The next cumulative backup is supposed to contain all the log files since the last full backup. It couldn't if the current backup were to result in deletion of some of the files.

I don't know the reason for #1.

Systems_Team
Moderator
Moderator
   VIP   

Hi Smith_Jones,

Just my 2 cents worth, as far as Exchange log truncation:

You don't say if you are using a standard Exchange backup, or if you are using VMware Intelligent Policies with Application State Capture for Exchange.  If you are using the VMware type policy for Exchange (with ASC), the manual says that your daily backups must be configured as Full, not incremental.

The VMware method above is what I'm using, and as every day is effectively a full you get daily log truncation.

Hope this helps,

Steve

Hi,

It is a standard Exchange backup. Standalone Exchange Servers in DAG.

VMware is not in the picture. 

Any reason w.r.t. below -  

For the 1st event, why it is saying so - "The following database is mounted,
although it will not be backed up: DAG1-DB02." Why? What is the meaning of it? The backup is successfully happening.

That's not our message. What's the event id? I suggest you google on it and find Microsoft's explanation.