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Incremental backups of DFSR data using Accelerator back up too many files

Article: 100014007
Last Published: 2014-09-15
Ratings: 1 0
Product(s): NetBackup & Alta Data Protection

Problem

It is possible and supported to backup Distributed File System Replication (DFSR) data in conjunction with Accelerator and observe the increased performance Accelerator is designed to deliver (See Related Article 000021195).

In some environments, the number of files and amount of data backed up is larger than it should be for a Differential Incremental backup job.

 

 
 

Error Message

During the pre-backup mode of a Differential Incremental DFSR backup, the bpbkar32.exe process receives the list of replicated folders from the DFS Writer, it then traverses the file system building a list of files to backup based on either the Archive Bit or Time and Date Stamp.  

If NetBackup detects that a file has not changed, it remarks that the file does not qualify to be backed up:

Example:
9:45:02.732 PM: [8068.15960] <4> dos_backup::tfs_scanstart: INF - in 'pre-backup' mode
9:46:05.732 PM: [8068.15960] <4> dos_backup::tfs_scannext: INF - <Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\Apps\myfile.txt> did not pass modification check

 

If NetBackup detects that a file has changed or is new, it adds the file to the backup set

Example:
9:47:05.661 PM: [8068.15960] <4> dos_backup::V_InitializeShadowCopy: INF - DFSRPath::mapShadowToNTFSMountPoint returned "C:\" for "Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\Apps\MyNewFile.txt" which was not already in the collection.
9:47:05.661 PM: [8068.15960] <4> dos_backup::V_InitializeShadowCopy: INF - FS_AddToSnapshotSet() (Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\Apps\MyNewFile.txt)

 

During the backup mode a Differential Incremental DFSR backup, the file-system is traversed by bpbkar32.exe a second time for backup.  At this point, the files on the file system are compared to the content of the Accelerator Track Log.  If an undocumented file is encountered, Accelerator forces a backup of the file - regardless of the state of the Archive Bit or Time and Date Stamp.

Example:
2:01:01.876 AM: [8068.15960] <4> dos_backup::tfs_scanstart: INF - in 'backup' mode
2:12:24.975 AM: [8068.15960] <2> dos_backup::fscp_change_detection(): DBG - file changed: could not find track journal entry for <Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\Apps\myfile.txt>

Cause

When VSS asks the DFS Writer for the list of replicated folders, it may not provide NetBackup the list in the same order each time.
 
The Accelerator track log is sensitive to file order.  Accelerator expects the file system will be traversed in the same order for every backup.  If Accelerator encounters a file that is not listed in the alpha-numeric order known to the Track Log it thinks the file hasn’t been backed up before, and treats it as a new file.
 
When the NetBackup builds the DFSR file list in a different order from job to job, Accelerator is unable to account for the inconsistent order, and subsequently backs up data which was included in the previous Differential Incremental backup.

Solution

There are two possible workarounds:

1. Discontinue use of Accelerator in a Policy which backs up DFSR data.

 

2. Leave Accelerator enabled, but in the Backup Selection of the Policy, specify by-name each replicated folder you would like backed up.

Example:

Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\Biology
Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\English
Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders\Psychology

 
 
Note: If new DFS Replicated Folders are created and need to be backed up, the newly created folders will need to be added to the Backup Selection of the Policy before they will be backed up.
 
NOTE: For steps on how to easily add DFSR Replicated Folder paths to a Policy, see Related Article 000021195.
 

Applies To

The issue exists when an Accelerator driven backup of DFSR data is performed with a broad backup selection such as:

ALL_LOCAL_DRIVES
or
Shadow Copy Components:\User Data\Distributed File System Replication\DfsrReplicatedFolders

 

References

Etrack : 3615305

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