If the expiration time of a backup image copy stored on a tape is manually changed to an earlier expiration time, the expiration time of the tape may be incorrectly changed to the same earlier time.

Article:TECH205819  |  Created: 2013-05-02  |  Updated: 2013-07-01  |  Article URL http://www.symantec.com/docs/TECH205819
Article Type
Technical Solution


Subject

Issue



An issue has been identified in NetBackup, where manually updating the expiration time of a backup image copy on a tape to a new expiration time, which is earlier than the copy's current expiration time, may also result in the expiration time of the tape being incorrectly changed to the same earlier expiration time.

This issue is rare.  It will only be experienced under specific circumstances (which are detailed in the Environment section) and cannot happen without manual action from a NetBackup administrator.

If a tape's expiration time is incorrectly changed to an earlier time, and the master server is running a version of NetBackup prior to 7.5, this may result in that tape being expired by NetBackup before some of the image copies that it currently holds are due to expire.  Expired tapes may then be overwritten, making any remaining valid images still on the tape unavailable for restore.


Environment



Scope of the Problem:

On a NetBackup master server (any platform) running any version earlier than NetBackup 7.5.0.6, a tape may be at risk of having its expiration time incorrectly changed to an earlier time if ALL of the following conditions are true:

  1. There are multiple backup image copies stored on the tape
  2. The image copies on the tape were written using multiplexing (MPX)
  3. All of the image copies on the tape were written as a single MPX group, which spans the whole of the tape, with no fragment break (Note: This is an unlikely circumstance - most multiplexed tapes contain multiple MPX fragments)

Tapes that may satisfy all of the conditions above can be identified by checking the output from the bpmedialist command.  A tape may only be at risk if the images value is set to 1, and the vimages value is set to MPX (as shown in the example below).  If either of the images and vimages values for a tape are different from these values, then the tape is not at risk of having its expiration time changed incorrectly.

id     rl  images  allocated       last updated     density kbytes restores
          vimages  expiration      last read        <------ STATUS ------->
---------------------------------------------------------------------------
A00000  8       05/12/2013 10:21 05/12/2013 14:47 hcart3    5701271     0
             MPX  04/01/2014 00:00       N/A       

If and only if a tape satisfies ALL three of the conditions above, then if the expiration time of one of the backup image copies on the tape is manually updated to an earlier time than the image copy's current expiration time, the expiration time of the tape will also be incorrectly changed to the same earlier expiration time.

Important: Updating an image copy’s expiration time requires administrator intervention by use of the bpexpdate command.  This issue cannot occur if there is no administrator action to manually change an image copy's expiration time to an earlier time.

This issue does not occur when the expiration time of an image copy is changed to a time which is later than the copy's current expiration time.

This issue does not occur when an image copy is set to expire immediately by using the -d 0 option on a bpexpdate command line.

This issue cannot affect tapes that hold non-MPX data (i.e. tapes that do not have the vimages value reported as MPX in the output from the bpmedialist command).

Consequences:

On a NetBackup master server running any version of NetBackup prior to 7.5, if a tape's expiration time has been incorrectly changed to an earlier expiration time under the circumstances explained above, this may ultimately result in it being expired too early by NetBackup, before the expiration time of one or more other valid image copies that the tape holds. After the tape is expired by NetBackup, it may become available to be allocated for new backups, and the un-expired image copies, which are still on the tape, may be overwritten by new backups, resulting in data loss.

On a NetBackup master server running any version of NetBackup 7.5 through 7.5.0.5, if a tape's expiration time has been incorrectly changed to an earlier expiration time, NetBackup will not actually expire the tape at the earlier time, if there are still valid image copies on the tape - NetBackup will only expire the tape after all of the image copies, which are still on the tape, have expired.  Hence, under NetBackup 7.5, there is no risk of the other image copies on the tape being overwritten by new backups. The tape is reported as "EXPIRED" by the bpmedialist command, but no valid backup data on the tape are at risk.


Cause



Under the certain specific circumstances mentioned above, when the expiration time of a backup image copy on a tape is being changed to an earlier expiration time by use of the bpexpdate command, a defect in NetBackup may cause the nbemm process on the master server to incorrectly change the expiration time of the tape to the same earlier expiration time as the image copy - even though there are other backup image copies on the same tape, which have a later expiration time.


Solution



The formal resolution for this issue (Etrack 3142241) is included in the following release:

  • NetBackup 7.5 Maintenance Release 6 (7.5.0.6)

NetBackup 7.5.0.6 is now available - please access the Related Article below for more information.

Workaround:
If it is not possible to upgrade the master server to 7.5.0.6, and image copy expiration times are being manually changed to an earlier time by use of the bpexpdate command, please contact Symantec technical support, referencing this document and one of the following Etracks to obtain an Emergency Engineering Binary (EEB) replacement containing a fix for this issue:

  • For NetBackup 7.5.0.5: 3191336
  • For NetBackup 7.1.0.4: 3185297
  • For NetBackup 7.0.1: 3185299

If the master server is running NetBackup 7.1.0.4 or earlier, and it is determined that there are tapes holding image copies satisfying the conditions described in this Alert, AND there has been administrative intervention to manually change image copy expiration times to an earlier time, then to identify whether any tapes holding valid images are currently at risk of being expired too early, run NBCC (NetBackup Catalog Consistency Utility - see Related Article linked below) on the master server.  It is recommended that all active backup and duplication jobs should be stopped or suspended before running NBCC.  If an inconsistency is detected by NBCC, open a new case with NetBackup technical support referencing this document ID to have the NBCC data analyzed for this problem.  Analysis of the NBCC data by NetBackup support will identify any tapes with an incorrect expiration time.  If any are detected, a repair will be provided to correct the expiration time of the tape.

Note: It is not necessary to run NBCC if the master server is running NetBackup 7.5 through 7.5.0.5 because of the behavior change in NetBackup 7.5 described above; media will not automatically be expired until after all of the image copies on the tape have expired, even if the tape has an expiration time that is earlier than one or more image copies that it holds.

Best Practices:
Symantec strongly recommends the following best practices:

1. Always perform a full DR backup prior to making any changes to your environment.
2. Always make sure that your environment is running the latest version and patch level.
3. Perform periodic "test" restores.
4. Subscribe to technical articles.

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Supplemental Materials

SourceETrack
Value3142128
Description

Expiration time of MPX media can be incorrectly changed to an earlier time - may eventually result in data loss




Article URL http://www.symantec.com/docs/TECH205819


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