Jamie,

   I did a lot of testing at one point trying to tune NetBackup for 
DSSU's, LTO2 and LTO3.

   I found that 1024 MB fragments would never even spin up the LTO3 
drive. It would basically start to speed up, then it would slow down 
because it had to position for the next fragment. Total time - 6 seconds!

   After much experimentation, I found that 6GB fragments worked best 
for LTO2 and 10GB fragments best for LTO3. (Local FC attached high speed 
disk to FC attached tape drives.) LTO4's could probably even use larger 
fragments, I never tested them.

   And to confirm what Ed says, given the speed of the tape drives, 
restores are not an issue. At most, even with 20GB fragments like Ed 
uses, you may spend an extra minute or two pulling the file off the tape.

     Bryan

-- 
Bryan Bahnmiller


JAJA (Jamie Jamison) wrote:
> So I just got a SpectraLogic T950 tape library, and after some initial
> teething pains it's up and running and it's wicked fast, but being an
> impatient little monkey of a NetBackup administrator I'm wondering if I
> could make it wicked faster.
>  
> My primary backups go to DataDomain restorers and then are duplicated to
> tape for offsite storage with Iron Mountain. When I set all of this up I
> used 2048 megabytes as the maximum fragment size in both the disk based
> and tape based storage units. This was based on my predecessor's
> experience with what was the best trade-off between backup speed and
> file restoration speed with LTO Gen 2 drives. But I'm wondering if I can
> improve backup performance even more by increasing the fragment size for
> my disk and LTO4 based storage units without degrading my current file
> restoration performance. I thought I would send this to the list to find
> out what people were using as the frag sizes on LTO4 and on disk based
> storage units such as the DataDomains. 
>  
> Also if I change the fragment size on my tape based storage units how
> does NetBackup handle tapes that have backups written to them with
> different fragment sizes. Can this cause problems? Any feedback will be
> greatly appreciated.
>  
>  
> Thank You,
>  
> Jamie Jamison
>  
> 
> 
> 
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> 
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