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Arun_K's avatar
Arun_K
Level 6
13 years ago
Solved

scan hosts

 

How the scan host is determined

EMM determines scan hosts; a scan host may be different for each shared drive. The first host in the environment to come online with a non-zero scan ability factor is the initial scan host for its drives.

To configure the scan ability factor of media servers, use thenbemmcmd command. For more information, seeNetBackup Commands Reference Guide.)

  1. scan ability factor is 2.Then will this hamper anything?
  2. scan ability factor is 0.What this means?
  3.  scan host are my media servers?
  • no they will work fine.

    just because a drive is down does not mean it is anything to do with the scan host.

    it is an impossible question "what if " I don;t know, it hasn't happened.

    NBU is too complex to guess at things that have not happened.

    That is my final answer on this subjust.

    Sorry, but Chris Zimmerman (more important than me) wants to put a stop to these 'what if' questions - this is not what the forum is for.

    The occassion question is fine, but not multiple "what if questions" in the same day.  The answers are all out there in the manuals, you just have to spend some time loking.

    Martin

     

     

     

  • No, here is a clue ...

    If the media servers all have the same scan vaule the first media server to grab the drives is the scan host

    So if you have 3 media servers with scan values 

    media1  = 9

    media2 = 5

    media3 = 5

     

    We know that media 1 should try and become the scan host, if it cannot, then we effectivly have this 

    media2 = 5

    media3 = 5 

    So, what do you think (the answer is in THIS post)

    Martin

  • @ Marriane:We have scan factor =5 on all our media serevrs.

     

    @Martin:so what if media 1 will not become the SCAN host then media 2 or media 3?

  • The answer is in the post directly above your question.

  •  

    Shared tape drive polling

    For shared tape drives, only the scan host polls drives until a mount request is received from NetBackup. During a mount request, NetBackup uses the host that requests the mount to poll the shared drive.

    This design enables NetBackup to support Dynamic Loop Switching or SAN zones. Each tape drive needs to be detected only from a single host. Each tape drive can potentially have its own scan host that switches dynamically to process errors and continue availability. A central device arbitrating component manages scan host assignments for shared drives. The arbitrating component also provides a network drive reservation system so that multiple NetBackup media servers can share a drive.

    Polling a shared tape drive allows dynamic loop switching and reduces the number of device accesses and reduces CPU time. However, it cannot detect connectivity breaks (for example, discontinuity in the Fibre Channel fabric) until I/O occurs.

    @Martin:Suppose my media 1 becomes the scan host and write now it is down.

    Will my al drives are non functonal then?

  • no they will work fine.

    just because a drive is down does not mean it is anything to do with the scan host.

    it is an impossible question "what if " I don;t know, it hasn't happened.

    NBU is too complex to guess at things that have not happened.

    That is my final answer on this subjust.

    Sorry, but Chris Zimmerman (more important than me) wants to put a stop to these 'what if' questions - this is not what the forum is for.

    The occassion question is fine, but not multiple "what if questions" in the same day.  The answers are all out there in the manuals, you just have to spend some time loking.

    Martin

     

     

     

  • Suppose my media 1 becomes the scan host and write now it is down.

    Don't stop reading the manual!

    See this topic: The scan host can change

    Please consider this thread as SOLVED (closed).

    Martin and I will no longer respond to any more questions.

    The manual really contains all the answers. You can verify the theory in the manual if you have a REAL environment by looking at vmdareq output on the master server...

    I WILL delete all further posts/questions in this thread since nothing else is adding any value.