A rare potential for data loss exists when using the NetBackup FlashBackup feature on a volume that has a very small cluster/block size, such as 512 bytes. Restores for Incremental backups performed by FlashBackup on this type of volume may result in the restoration of corrupt files, but the restore completes with a Status 0 (Successful).

Article:TECH65738  |  Created: 2008-01-04  |  Updated: 2013-10-24  |  Article URL http://www.symantec.com/docs/TECH65738
Article Type
Technical Solution

Product(s)

Environment

Issue



A rare potential for data loss exists when using the NetBackup FlashBackup feature on a volume that has a very small cluster/block size, such as 512 bytes. Restores for Incremental backups performed by FlashBackup on this type of volume may result in the restoration of corrupt files, but the restore completes with a Status 0 (Successful).

Solution



Introduction:
A rare potential for data loss exists when using the NetBackup FlashBackup feature on a volume that has a very small cluster / block size, such as 512 bytes.  If a restore is done on Incremental backups performed by FlashBackup on this type of volume may result in the restoration of corrupt files, but the restore completes with a Status 0 (Successful).

Both a formal resolution and a workaround are available to prevent this issue from occurring to allow data to be restored correctly from backups that are potentially affected by this issue.


What is Affected:
The following NetBackup versions are affected, on all supported Master Server platforms*:
-  NetBackup Server/Enterprise Server 6.0 GA through 6.0 Maintenance Pack 7 (MP7)
-  NetBackup Server/Enterprise Server 6.5 through 6.5.2A

* Versions prior to 6.0 (on supported platforms) are also affected by this issue if the conditions below are met.  Please note that these versions have reached the End of Engineering Support date and no future patches are planned for those versions.  It is recommended that affected users of these older versions apply one of the workarounds below, then upgrade to NetBackup 6.x as soon as the formal resolution is available.


How to Determine if Affected:
Data loss has been known to occur if ALL of the following conditions are met:
- A 512-Byte block size is being used for the volume on a client (refer to Note below)
- A full backup is run on this volume using NetBackup FlashBackup
- A subsequent incremental backup is run
- Files are restored from this incremental backup in a corrupt state, due to this issue
- The corrupt data goes unnoticed and is required at a later time, but the required backup set(s) have become expired and are overwritten.

Note: This issue has only been observed on volumes with a 512 Byte cluster / block size.  It is possible that this issue could also be seen on other cluster sizes that are very small, or non-standard.   However, this has not been reported or reproduced internally.


Formal Resolution:
This issue is formally resolved in the following patch:
- NetBackup Enterprise Server 6.5.3 (Currently Available).

This release is available at the following link:
 http://seer.entsupport.symantec.com/docs/315028.htm

This formal resolution will allow restores to take place without corruption if the conditions described in the document are met.  If the formal resolution cannot be applied, Symantec strongly recommends implementing the workaround in the next section.


Workaround:
Performing a raw partition restore of a backup that meets the conditions described above will allow data to be restored without any corruption.  

Also note that applying a formal resolution (mentioned below) will allow recovery of backups that meet the above conditions.

Symantec Strongly Recommends the Following Best Practices:
1. Always perform a Full backup prior to and after any changes to your environment.
2. Always make sure that your environment is running the latest version and patch level.


How to Subscribe to Software Alerts:
If you have not received this TechNote from the Symantec Email Notification Service as a Software Alert, please subscribe at the following link:    http://maillist.entsupport.symantec.com/subscribe.asp


Supplemental Materials

SourceETrack
Value1394039
DescriptionETrack (NetBackup): 1394039 NetBackup VMWare Backups corrupt vmdk files because it is changing the head of the VMDK file.

Legacy ID



315740


Article URL http://www.symantec.com/docs/TECH65738


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