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How netbackup chooses media (Complete this list)

felonious_caper
Level 5

Alright, not that I'm having any issues but this is out of pure curiousity fueled by my OCD. I'm trying to understand what criteria netbackup uses when selecting new media to be written to. So far I know the following.

1.) Is there an active and already assigned media in the required volume pool?

2.) Is there an active and non assigned media in the required volume pool?

3.) Is there an active and non assigned media in the scratch pool?

 

what other criteria is used beyond that point? last mount? total mounts? etc...

1 ACCEPTED SOLUTION

Accepted Solutions

J_H_Is_gone
Level 6

http://www.symantec.com/business/support/index?page=content&id=TECH35407&actp=search&viewlocale=en_U...

 

your #4 if more than one volume qualifies, Media Manager chooses the volume that was least recently used. NetBackup then adds it to the media catalog and assigns it the specifiedretention level.

 

LEAST Recently used - if one tape had mounts and one tape did not - then the one with no mounts is the "least recently used"

from the tech doc

VERITAS NetBackup (tm) tries to load balance tape usage, favoring media with the fewest mounts assigned first. When a new tape is added with zero mounts assigned, that tape would be a prime candidate for use first. In some installations with smaller tape libraries, it may be desirous to first fill the older media prior to writing to the new unwritten tapes, the end result being, those older media can be filled and replaced, maximizing tape usage.
 

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19 REPLIES 19

felonious_caper
Level 5

what you just posted is exactly what I have written above. My question is, what criteria is used AFTER netbackup decides it needs to pull media from scratch.

J_H_Is_gone
Level 6

is the tape full  - then do not choose it

is the tape frozen or suspend - then do not choose it

do you allow mixed retentions on the same tape

   say you do NOT - and you have one tape with 2 week retention on a tape ( RL 1)

                              and a tape with 6 month retention  on a tape (RL 6)

and you are trying to do a 2 week backup - then the first tape would be used for the backup and not the second tape.

if you have put a expiration on the PHYSICAL tape like max mounts or a date and it has reached that - the it would not pull that tape for a backup.

felonious_caper
Level 5

Ok but there is no criteria for once netbackup has determined that a scratch tape must be used?

mph999
Level 6
Employee Accredited

Ahh, sorry - it wasn't too clear ...

Hopefully this TN is more detailed ...

http://www.symantec.com/business/support/index?page=content&id=HOWTO32854

Martin

J_H_Is_gone
Level 6

 it tries to do load balancing by chosing the tapes with the lowest number of mounts

 

mph999
Level 6
Employee Accredited

Hmm, I'm not sure it goes on the lowest number of mounts ... from the documentatiom:

(Note, this is from an older manual - I couldn't find it in the 7.x manuals, but I'm not aware it has changed).

 

If the media catalog does not have a suitable volume, NetBackup requests MediaManager to assign one. Also, if a volume is at EOM (end of media), NetBackup willrequest a new volume. This may happen even if the volume is not completely full(because NetBackup received an EOM message from the drive).Media Manager assigns a volume to NetBackup that meets all of the followingcriteria:
 
Is the correct media type.
 
Is for the correct robot type (if applicable).
 
Is located in the requested robotic peripheral (if applicable).
 
Resides on the requested host.
 
Is in the correct volume pool.
 
Is not currently assigned (not already allocated to NetBackup).
 
Is not expired (if an expiration date is defined in Media Manager).
 
Has not exceeded the maximum number of mounts allowed.
 
4.
If more than one volume qualifies, Media Manager chooses the volume that was least recently used. NetBackup then adds it to the media catalog and assigns it the specifiedretention level.
 
5.
If there are no unassigned volumes of the requested type, the backup terminates withan error indicating that there was no available media.
 
Martin

J_H_Is_gone
Level 6

http://www.symantec.com/business/support/index?page=content&id=TECH35407&actp=search&viewlocale=en_U...

 

your #4 if more than one volume qualifies, Media Manager chooses the volume that was least recently used. NetBackup then adds it to the media catalog and assigns it the specifiedretention level.

 

LEAST Recently used - if one tape had mounts and one tape did not - then the one with no mounts is the "least recently used"

from the tech doc

VERITAS NetBackup (tm) tries to load balance tape usage, favoring media with the fewest mounts assigned first. When a new tape is added with zero mounts assigned, that tape would be a prime candidate for use first. In some installations with smaller tape libraries, it may be desirous to first fill the older media prior to writing to the new unwritten tapes, the end result being, those older media can be filled and replaced, maximizing tape usage.
 

mph999
Level 6
Employee Accredited
That confirms it then, without seeing the tn you found I would say least recently used would be based on dates not number of mounts, good find on the tn .

J_H_Is_gone
Level 6

a scratch tape has no date - the only thing NB knows is the number of mounts.

 

mph999
Level 6
Employee Accredited

That's a very good point ..

M

Andy_Welburn
Level 6

if it's an 'old' scratch tape (i.e. moved to scratch once data expired) as opposed to a brand new one, it will have a last mount date/time......

felonious_caper
Level 5

so maybe it uses a combination of last mount date AND number of mounts?

Andy_Welburn
Level 6

I'll try testing it tomorrow - I've got about 300 scratch tapes to choose from ranging from 4 to 61 mounts (plus I'm sure I could arrange a 0 mount too!) & a last mount from 26/11/09 (if I can find it) to 09/03/12 so maybe we'll end up with a definitive answer (or not)

J_H_Is_gone
Level 6

VERITAS NetBackup (tm) tries to load balance tape usage, favoring media with the fewest mounts assigned first.

 

so to test it I have tapes with 0 mounts and tapes with mulit mounts (they also have last mount times) in the Scratch pool

I set up a test policy and a test volume pool (no tapes in the volume pool)

started the backup

it took the first tape with 0 mounts from the Scratch Pool.

 

Andy_Welburn
Level 6

... after doing numerous tests I found that it used the oldest tape (except once where a media was selected slightly out of sequence) from the volume pool concerned - until I realised we were supposed to be looking at what tape it pulled from scratch -DOH!

A much quicker test later & as far as our set-up is concerned the media pulled from scratch appeared to be totally random. We had 0 mount "new" tapes amongst many many others in our scratch pool & NB chose one that had 25 mounts (from a range of 0 to 52 mounts) with quite a recent creation date & last mount time relative to all the others. Next time up took one with 27 mounts, a much older creation date & last mount.

So, for us at least,  there appears to be no logic in what gets pulled from scratch, which isn't what I expected following Judys tests & certainly when there appears to be some form of logic in the other selection processes .....

J_H_Is_gone
Level 6

I wonder if it also takes into account who last owned the tape - when you have mulit media servers

felonious_caper
Level 5

The tape library may also play a part in this, as some have options to load tapes sequentially or randomnly. Did the "slot" number play a role in which tapes were picked?

Andy_Welburn
Level 6

That was one thing I didn't make a note of & am now at home so can't check!