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scan hosts

Created: 05 Oct 2012 • Updated: 05 Oct 2012 | 17 comments
This issue has been solved. See solution.

 

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?

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Marianne's picture

Please show us output of 'vmdareq' on your master server.

It is easier to explain when we compare info in the manual with output in your environment.

The media server with highest 'scan ability' value will be the preferred scan host. 
Each drive will have one SCAN host.

The media server that is started first is normally the SCAN host for all shared drives.

'scan ability' of 0 means you don't want that particular host to be the scan host for any of the drives.
The default value is 5 on all media servers. 

Your extract from the manual says exactly that:

The first host (media server) in the environment to come online (started first) with a non-zero (higher than 0) scan ability factor is the initial scan host for its drives.

(Rest of the section in SSO manual is also very useful...)

 

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

Arun K's picture

The media server with highest 'scan ability' value will be the preferred scan host.

 

What will hapeen in this case.

i have 3 media servers and 10 drives.All are shared.What this means in case of SCAN host.

mph999's picture

Type.

"netbackup scan host" into google, top answer is :

http://www.symantec.com/docs/HOWTO32788

"The media server with highest 'scan ability' value will be the preferred scan host.

What will hapeen in this case.

i have 3 media servers and 10 drives.All are shared.What this means in case of SCAN host."

 

We are not getting into 'what/ if' questions - is there actually an issue ?, if not, leave things alone and do not change settings.

Everything you need to know about scan host is in the link I mentioned.

If things are runnign and you have no issues, theer is no problem.  If you do have a real problem, then let us know.

On a system your size, the default settings should be fine, or what every yours settings are fine if things are working.

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
Marianne's picture

Please read through my previous post again. 

I promise you - the answer is there. Really.

Please also post output of vmdareq command.
This will show us how the theory in the manual is applied in YOUR environment.

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

mph999's picture

Exactly what it says. - Read it again the answer is there.

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
Arun K's picture

The media server with highest 'scan ability' value will be the preferred scan host. 
Each drive will have one SCAN host.

 

What abt the other media servers with low scan factor?

Marianne's picture

Nothing.

Question already answered.

3rd request:

Please post 'vmdareq' output.
This will show you 'what about' other media servers.

 

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

mph999's picture

If the media server with the highest scan ability  value is the preferred one, what do you think this means about the others ...

 

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
Arun K's picture

Others will not use the drive

Marianne's picture

If you had a REAL environment, you would know that this is NOT the case.
Is that why you keep on ignoring my request for vmdareq output?
Just another theoretical question?

If you read further in the manual (as per my suggestion above) you will see what the real purpose of a Scan Host is. See: Shared tape drive polling.

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

mph999's picture

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

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
Arun K's picture

@ 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?

Marianne's picture

Answered in this post: https://www-secure.symantec.com/connect/forums/scan-hosts#comment-7798261

I need you to answer these questions as well, please: https://www-secure.symantec.com/connect/forums/scan-hosts#comment-7798361

 

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

mph999's picture

The answer is in the post directly above your question.

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
Arun K's picture

 

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?

mph999's picture

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

 

 

 

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
SOLUTION
Marianne's picture

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.

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links