NetWorker: Incremental file system backup on Windows appears to backup same files that were previously backed up without changing

Summary: NetWorker: Incremental file system backup appears to backup same files that were previously backed up without changing.

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Symptoms

  • NetWorker Client Windows file system backup.
  • When backing up Windows clients with scheduled level  incr, you should note that *Any* file which is renamed since last backup of that file, will then be backed up *again* in the next incremental.  
  • In an environment where either applications, scripts, perhaps end users are regularly renaming files, this can cause many *unchanged* files to be backed up again by design.
  • Incremental file system backups for a Windows client (for example, level = incr), appears to backup the same files that were not changed since the previous backup. 


Observations:    

  • mminfo -avot -c clientname 
shows the size of the incr backup almost same. The same as full backup.
  • nsrinfo -V clientname  > clientname_nsrinfo.out 

-V (uppercase) shows files backed up, and their respective backup date and mtime, atime, ctime.

Check nsrinfo to find files which were backed up on two or more dates where each backup has same mtime as the first backup date. 

Cause

If a Windows client has an environment where applications, or scripts, or end users are regularly renaming files, this can cause many *unchanged* files to be backed up again by design. 

Resolution

To avoid renamed files being backup again by Incremental backup, Limit renaming files and this will not happen.

However, when files are renamed frequently and only if the intent is to not backup those renamed files, on the Windows Client do the following:   

1. Log in as a Windows Administrator on the client. 
2. Create a SYSTEM ENVIRONMENT VARIABLE.
SYSTEM  ENVIRONMENT VARIABLE   
Name          :    NSR_AVOID_ARCHIVE
Value         :    yes 
 
3. Restart nsrexecd service (for example, NetWorker Remote Exec service) before the next incremental backup. 
net stop nsrexecd
net start nsrexecd 

Additional Information

Per NetWorker documentation:    

On Windows, file modification/change time refers to Last Written time, Creation time, and the Archive file attribute of a file. All these are used to determine whether a file must be backed up.

If the Archive file attribute is set, the file will always be backed up, since some older file systems may not have the proper file creation time, unless NSR_AVOID_ARCHIVE environment variable is set (to a value other than "no").

Notes:    

  • mtime, is Modified Time
  • ctime, is Create Time
  • atime, is Last Accessed Time 
  • If a new file is created, the ctime and mtime are identical.
  • If a file is modified again, the mtime is updated.
  • Also, specifically for Windows operating system, when a file is modified in ANY way - the Archive Bit is Enabled.  
  • In Windows, Modified includes:   
    • Creating a new file
    • Modifying contents of a file
    • Modifying the Archive bit manually with ATTRIB commands
    • Renaming a file name - also enables archive bit attribute.
  • Note: When a file in Windows is Renamed, this Enables the archive bit.
A simple way to see all these attributes in a Windows folder, is to use a Powershell command such as the following cmdlet which displays:   

Mode, LastWriteTime , Length (also known as size) , Name.

Note: The mode displays -a-  if the Archive Bit attribute is Enabled like the example.

PS C:\tmp> ls .\readme.txt
   Directory: C:\tmp
Mode                LastWriteTime         Length Name
----                -------------         ------ ----
-a----        3/25/2020   5:27 PM              8 readme.txt

The following example further shows nsrinfo -V clientname where:    

file1.dat and file2.dat were both backed up twice in one day.

But mtime for each file was the same in each backup implies the file was not modified and expected the files Not be backed again the second time.
 

Path\File1.dat, size=38947302608, off=12821900, app=backup(1),
date=1585064436 Tue 24 Mar 2020 11:40:36 AM EDT, mtime=1584848135 Sat 21 Mar 2020 11:35:35 PM EDT,
atime=1584846900 Sat 21 Mar 2020 11:15:00 PM EDT, ctime=1584846900 Sat 21 Mar 2020 11:15:00 PM EDT

Path\File2.dat, size=6878417744, off=312074829280, app=backup(1),
date=1585064436 Tue 24 Mar 2020 11:40:36 AM EDT, mtime=1585019905 Mon 23 Mar 2020 11:18:25 PM EDT,
atime=1585019700 Mon 23 Mar 2020 11:15:00 PM EDT, ctime=1585019700 Mon 23 Mar 2020 11:15:00 PM EDT

Path\File1.dat, size=38947302608, off=12841656, app=backup(1),
date=1585026274 Tue 24 Mar 2020 01:04:34 AM EDT, mtime=1584848135 Sat 21 Mar 2020 11:35:35 PM EDT,
atime=1584846900 Sat 21 Mar 2020 11:15:00 PM EDT, ctime=1584846900 Sat 21 Mar 2020 11:15:00 PM EDT

Path\File2.dat, size=6878417744, off=312074849036, app=backup(1),
date=1585026274 Tue 24 Mar 2020 01:04:34 AM EDT, mtime=1585019905 Mon 23 Mar 2020 11:18:25 PM EDT,
atime=1585019700 Mon 23 Mar 2020 11:15:00 PM EDT, ctime=1585019700 Mon 23 Mar 2020 11:15:00 PM EDT

Affected Products

NetWorker

Products

NetWorker
Article Properties
Article Number: 000170137
Article Type: Solution
Last Modified: 29 Sept 2023
Version:  3
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