NBU 6.5 - Media Multiplexing - the dangerous level 1

[Alexandre_Rappo]

Hi all,

I have searched the forums this morning around multistreaming and multiplexing (MDS and MPX) and I was surprised not to find anything about the media multiplexing level parameter controlled by policy and schedule.

Media Multiplexing definition:
  "This parameter will control how many jobs/streams the class can multiplex on one drive". Source http://support.veritas.com/docs/294159 
  The class being here the logical group configured through the policy and schedule.

Media Multiplexing behaviour:
  Level 1 (danger!): set the level to 1 and it will result in an EXCLUSIVE behaviour from your backup job, as it requires a tape drive to itself. Tested behaviour will see the job being queued until a tape drive is not in use or job will be active with no other jobs multiplexed onto the tape drive. Obvious consequences: backup window explosion, poor infrastructure utilization and performances, drive shoe-shining...
  Level x ≥ 2 (ok!): set the level at 2 or higher (drive multiplexing limit) and the backup job will happily join in the other active jobs onto the same tape drive. I need to do more testing to see how well the level is respected.

Conclusion: 
  Media Multiplexing level 1 really should be corrected to 0, as it enforces an EXCLUSIVE behaviour: one UNIQUE backup job at the time onto one Tape Drive.

I will update the thread with the results of additional tests, but feel free to confirm that you got the same results, as I am a bug collector. ;)

Kind regards,

Alex Rappoport

[rjrumfelt]

For any level greater than 1, multiplexing can have an impact on restoring data when comparing multiplexed vs non-multiplexed backups.

[J_H_Is_gone]

Funny how different people see things differently.

for me Media Multiplexing level 1 means only 1 job at a time.
level 2 means 2 jobs
level 8 means 8 jobs

To me that is the known and expected action.

[Alexandre_Rappo]

Well I disagree,

the very definition of multi is 2 or more. Disabling multiplexing by the value 1 is misleading.
So best of worlds for NBU would be to have 0 as 'no multiplexing' and 2 or higher for multiplexing. Or the term to be changed to 'Media Plexing'.

You can guess the NBU answer for no multiplexing is 1 as for some STU types like disks, NBU will grey out the parameter...

Semantic @ Symantec !!

[Marianne · Accepted solution]

Have you had a look at chapter 1 of NBU Admin Guide II? It explains multiplexing in detail with diagrams and examples.
You can disagree or just accept the way it works - the choice is yours...