ProblemWhen backing up data residing on NTFS Deduplication enabled volumes, while using Accelerator, there is a limitation in the way NetBackup can use the Windows Change Journal to identify and backup changed files within a given backup selection.
This limitation will result in the following messages appearing in the Activity Monitor Job Details:
08/03/2017 13:15:34 - Info bpbkar32 (pid=1216) not using change journal data for <G:\>: hard link or reparse point change detected
08/03/2017 13:15:34 - Info bpbkar32 (pid=1216) not using change journal data for enumeration for <G:\> but will use it for change detection
The implication of the above message " not using change journal data for enumeration" means the bpbkar32.exe process must walk through all files within the Backup Selection and interrogate each file to determine if the file has changed. When there are many files, the process of examining each file can take time and cause incremental backups to run longer than expected.
Conversely, when the Windows Change Journal is used for enumeration, the Change Journal passes the exact list of changed files to NetBackup, and bpbkar32.exe surgically backs up just those changed files. No other files are examined.
As noted in the Job Details log snip above, given this constraint, NetBackup (versions 8.0 and earlier) is not able to utilize the Windows Change Journal to enumerate the list of changed files within the Backup Selection. The bpbakr32.exe process must evaluate each file to determine if a change occurred and react accordingly.
NetBackup engineering has determined there is a way to enable NetBackup to use the Windows Change Journal for file list enumeration on NTFS volumes with deduplication enabled.
By enabling this functionality, the Change Journal gives NetBackup the exact list of changed files since the last backup job, and NetBackup examines and protects only those specific files.
This functionality is present NetBackup 8.1.1 and later versions.
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