so that's disk *access* time not necessarily disk throughput..  one guess 
is that when you multistream from one disk to two drives (each drive 
accepting two streams) netbackup is going to have to bounce between 
writing stream 1 and writing stream 2.. it's not a very intelligent 
streaming mechanism if I'm remembering correctly..  

because it's just load balancing time between the two streams, the disk is 
having to constantly switch the location where it's reading it's data -- 
therefore increasing the overall access time.  

when you do one stream per tape drive it simply streams the data straight 
through until it's done.  as soon as you do multiplexing you start causing 
this type of behavior where the disk head is going to have to bounce 
around between two areas which will increase those vxstat statistics..

just an idea,

Jon

On Thu, 14 Nov 2002, Mark Evangelista wrote:

> One plausible explanation is that multithreading is keeping your tape speeds
> up which will improve throughput.
> 
> "W. Curtis Preston" wrote:
> 
> > Instead of sending 10 streams to 10 tape drives, we're sending 10 Oracle
> > streams
> > to five tape drives.
> >
> > The DBAs are claiming that vxstat shows that disk access times have shot
> > up significanly during backups, and this doesn't make any sense to me.
> > Does anybody have any idea why this would be the case?
> >
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