NetBackup will use drives for backup based on (at least) the
following:

1) Number of streams queued (if you look in the Activity Monitor,
   every backup job is a separate stream)

2) Number of drives configured in the storage unit definition(s)

3) Level of multiplexing (set at STU definition and schedule)

4) Retention of schedules (will not mix retention levels on single
   tape by default)

5) Max jobs per class (class definition)

6) Max jobs per client (global configuration, possibly tunable on a
   per client basis???)

For restore, NBU doesn't care about most of this, and will use as many
drives as it can (one per restore job submitted, except under certain
circumstances when it's restoring from multiplexed backups).


If you don't use multistreaming, each you'll get a separate backup
stream for each client in each class.  If you do use multistreaming,
you can get multiple streams for each client in a class.  You'd use
this if you had client(s) with multiple volume/disk groups and you
wanted to get each volume group running at the same time.  Another
benefit is that if a job fails, it only needs to restart the stream,
not the entire class/client backup.

You almost surely don't want to have multiple streams running on the
same set of disks at the same time.

Multiplexing is allowing multiple streams to write to the same drive
at basically the same time.  You'll probably have to do this to get
the maximum usage from your LTO's.

Mutlistreaming and multiplexing are not mutually exclusive, you can
combine them in all sorts of interesting ways.


You may want to do some things with your SAN configuration so that
each drive can be seen via only one HBA at a time.  Hopefully someone
with more details can jump in on this one.


Unless your media server has a lot of really fast filesystems (on
separate volume groups) on it, or you've got a really nice network
coming into it (at least two Gb or the equivalent), you probably don't
need to worry about scheduling jobs to use all eight drives at once.
You want to find the slowest piece of the backup process, and improve
it (repeat as necessary).


Ryn writes:
> Hello folks,
> 
> We have a media server with two Qlogic FC-AL adaptors attached to a brocade
> switch. There
> are eight LTO drives hooked up to the media server (through the switch). If I
> create a class, and
> want the class to utilize all eight drives, do I have to enable multiplexing 
> of
> jobs? Will Netbackup
> use all eight drives for client backup/restore under normal circumstances? I 
> am
> trying to configure the
> system to make the best use of the drives.
> 
> Thanks for any info.
> 
> - Ryn
> 
> 
> _______________________________________________
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-- 
Larry Kingery 
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