04-09-2012 08:17 AM
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...
Solved! Go to Solution.
04-09-2012 12:43 PM
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.
04-09-2012 08:44 AM
04-09-2012 08:52 AM
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.
04-09-2012 09:15 AM
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.
04-09-2012 10:16 AM
Ok but there is no criteria for once netbackup has determined that a scratch tape must be used?
04-09-2012 10:29 AM
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
04-09-2012 10:31 AM
it tries to do load balancing by chosing the tapes with the lowest number of mounts
04-09-2012 11:25 AM
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).
04-09-2012 12:43 PM
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.
04-09-2012 01:17 PM
04-09-2012 01:58 PM
a scratch tape has no date - the only thing NB knows is the number of mounts.
04-10-2012 04:04 PM
That's a very good point ..
M
04-11-2012 12:13 AM
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......
04-11-2012 07:57 AM
so maybe it uses a combination of last mount date AND number of mounts?
04-11-2012 08:03 AM
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)
04-11-2012 11:29 AM
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.
04-12-2012 01:19 AM
... 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 .....
04-12-2012 09:21 AM
I wonder if it also takes into account who last owned the tape - when you have mulit media servers
04-12-2012 09:46 AM
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?
04-12-2012 09:59 AM
That was one thing I didn't make a note of & am now at home so can't check!