You are correct.  Of course, the storage unit depicts the number of streams
utilized to tape and the schedule allows the backup to be multiplexed.  When
client schedules are initiated with the multiplex option, they are simply
placed in the que and utilize the storage units MPX settings accordingly
(1st come, 1st served).  Running a backup to multiple tapes is considered
Multiple Data Streams, not MPX, but they too have to abide by the storage
units MPX settings and whether the schedule/policy will allow them to be
multiplexed.  This does not necessarily mean the streams will be multiplexed
to the same tape either, that depends on the job que...

Matthew Moody

-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu]On Behalf Of Fabbro,
Andrew P
Sent: Monday, January 27, 2003 1:15 PM
To: 'Brian Chase'
Cc: veritas-bu AT mailman.eng.auburn DOT edu
Subject: RE: [Veritas-bu] Considering moving to NetBackup


>When using MPX, you're splitting the stream across multiple drives. Did you
have multiple drives available (and occupied)
>by the MPX'ed tapes that were being copied to the non-MPX offsite?

I don't think that's correct.  MPX allows you to combine multiple data
streams onto one drive.

So if you had:

        client1 with 2 streams (i.e., two filesystems, configured as
separate streams)
        client2 with 3 streams
        client3 with 3 streams

and an MPX of 6, one drive would handle all streams from client1 and
client2, and one stream from client3.  The other 2 streams from client3
would go to other drives (or wait if there were no other drives available).
On the tape, you would see blocks from all 6 streams mixed together (2 from
this stream, 3 from that one, 1 from this one, etc.)

The purpose of multi-plexing is to keep modern drives streaming.  If a drive
receives sufficient data that doesn't have to pause and reposition (aka
"shoe-shining"), the write speed is greatly improved.  When a vendor quotes
you a write speed, the assumption is that the drive is streaming (and sneaky
vendors always assume highly compressable data, but that's another post ;)

NetBackup CAN split a backup that consists of separate streams to multiple
drives (one stream to this drive, one stream to that drive).  But there is
nothing that splits a single stream over multiple drives.

--
 Drew Fabbro [fabbro.andrew AT cnf DOT com]
 Unix Systems Group
 Desk: 503-450-3374
 Cell: 503-701-0369
_______________________________________________
Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu