Restores from non-optimized backups of NTFS Deduplication volumes may appear to succeed, but the restored data is corrupt.

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Description

Restores from non-optimized backups of NTFS Deduplication volumes may appear to succeed with status code 0 reported, but the restored data is corrupt.

This issue occurs only when Enterprise Vault is installed on the client machine and a non-optimized backup is taken for NTFS Deduplication volumes.

The combination of NTFS Dedup and Enterprise Vault causes this issue resulting in an incorrect backup ultimately leading to data loss.

Support for protecting Windows 2012 as NetBackup clients started in the 7.5.0.6 maintenance release.  New with Windows 2012, it is possible to configure Data Deduplication on an NTFS file system.

Microsoft supports placing DFS Replicated folders on NTFS Deduplication volumes.

NetBackup supports backing up / restoring this combination as well (DFSR Data on NTFS Deduplication volumes) 

It may be observed that backing up deduplicated DFSR data results in abnormally small backup sizes.  Restores from these backups will result in normal looking but unusable files.

bpbkar logs shows the backup image size less than the file data: 15:16:00.527 [15392.13652] <2> tar_base::backup_finish: TAR - backup:                     25 files
15:16:00.528 [15392.13652] <2> tar_base::backup_finish: TAR - backup:          file data:  139193275 bytes
15:16:00.528 [15392.13652] <2> tar_base::backup_finish: TAR - backup:         image data:     250880
15:16:00.528 [15392.13652] <2> tar_base::backup_finish: TAR - backup:       elapsed time:         92 secs         2726 bps

Upon attempting to access a restored DFSR file, when the file is restored to an alternate volume, the following messages may be observed in the following situations. 

1. When attempting to open an affected file - for example:


Windows Photo Viewer can't open this picture because the file appears to be damaged, corrupted, or is too large.

2. When attempting to copy an affected file - for example:


An unexpected error is keeping you from copying the file. If you continue to receive this error, you can use the error code to search for help with this problem.

Error 0x80070780: The file cannot be accessed by the system.

3. When attempting to delete an affected file - for example:


An unexpected error is keeping you from deleting the file.  If you continue to receive this error, you can use the error code to search for help with this problem.

Error 0x80070780: The file cannot be accessed by the system.

This issue has the potential to affect Windows 2012 clients from versions 7.5.0.6 to 7.7.3 where Enterprise Vault is also installed.

This issue affects all DFSR deduplicated data.  Data is incorrectly backed up, even though a successful status may be reported in the Activity Monitor.  If incorrectly backed up data is then "restored," the resulting files will appear to be successfully restored (and a successful restore will be reported) but the "restored" data will be unusable.

Additional details and conditions:

  • Windows deduplication is only supported on Windows 2012 Server or 2012 R2 Server.  Backups of data on other operating systems should not have a problem.
  • This only applies to DFSR data.  There should be no problem with backing up any other data, even data on the same volume.
  • This only applies to non-optimized backups.  Optimized backups should still work properly.
  • The DFSR data must be on a Windows deduplicated storage volume.  Backups of DFSR data on any other type of volume should have no problem.
  • For a backup to be exposed to the problem files in the backup must actually be deduplicated.  Not all files on the volume are deduplicated and of those that are, some time is needed before a file is actually deduplicated.  Any normal, non-deduplicated file should be backed up without problem.

Note: Files smaller than 32 KB are not deduplicated at all.  However, any DFSR data which is not deduplicated (for whatever the reason - timing, deduplication excludes, etc) will be handled correctly.

There are two scenarios of concern with this issue which could result in data loss, for sites which fit the above conditions.  The difference is whether or not a damaged backup has been used to restore DFSR data.

1. Any existing backups of data fitting the above conditions should not be used.  It is recommended that a full backup be performed as soon as possible after a fixed version of NetBackup has been installed on the DFSR client.

2. If a damaged backup is used to restore DFSR data to the original location, some restored deduplicated DFSR files may still be usable while others may not.  The extent of the damage is proportional to the amount of change that has occurred on the volume between the backup and the restore.

Additional Note:
When the issue has occurred during backup, the reported Kilobytes (size of the backup job) will be much smaller than it should be.  In the below example, a single 5 MB file was backed up.  The bottom job reflects the backup size as it should be (5079K); the top job shows the size when the issue has occurred (only 58K).   On a large data set, the final KB count could be remarkably smaller than expected.

Action Required

The formal resolution for this issue (Etrack 3892790) is included in the following release:
  • NetBackup 8.0
Download and README information about this release can be found by accessing the following link:  https://www.veritas.com/content/support/en_US/15143.html

Workaround:
If upgrade to a resolved version is not feasible, contact Veritas technical support, referencing this document and Etrack 3905488 to determine Emergency Engineering Binary (EEB) availability.

Related Articles

The NetBackup 8.0 GA Release is a full media release for upgrades from any NetBackup 7.x version.

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