Conference 7.286::fddi

476.0. "FDDI-Performance for Backup" by MUDIS3::REPPERMUND () Thu Feb 13 1992 08:07

Our customer has 4 VAX-Systems (1 Cluster) installed at a large 
manufacturing plant. 
Now they want to install a StorageTek tape silo for backup
and archiving purposes. All 4 systems shall be backuped into this
silo. 
We are proposing a solution, where we connect one of these systems 
(in this case a VAX 9000/210) with the silo via XMI-Interface 
(Polecat). The software for managing the silo access is DCSC and SLS.

In this scenario the backup of the other 3 systems shall be done
over FDDI and over the VAX 9000/210 into the silo.

For better understanding a picture:



				FDDI
	==========================================================
	    !	 	    !	 	    !		    !
	    !	 	    !	 	    !		    !
	    ! Cluster 	    ! 		    !  		    !
   	*-------* 	*-------*	*-------*	*-------*
	!	!	!	!	!	!	!	!
	! 9000/	!	! 6420	!	! 6420	!	! 6320	!
	!  210	!	!	!	!	!	!	!
	!	!	!	!	!	!	!	!
	!-------!	*-------*	*-------*	*-------*
	!  XMI	!	
	*-------*		
	    !
	    ! STI/FIPS
	    !
	    !
	*-------*
	!	!
	! STK	!	
	!  Silo	!
	!	!
	*-------*


We do known the throughput of the different interfaces very well
(STI, KDM70, HSCSX, CIXCD, TA90) for the standalone variant 
(Backup of the VAX9000/210 alone directly into StorageTek). Without any 
optimization we get about 1 MB/sec in case of a standalone 9000/210 
and only 1 backup stream. This was measured by the customer and 
recognized. The limiting factor in this case are the discs (RA90). 

What we don't know: If we backup the other system over FDDI and the 
9000/210 into the silo, what is the maximum bandwith of the 
FDDI-connection in this case? Is FDDI the new bottleneck of this 
configuration when we use more streams, use a lot of performance
enhancements (disc-shadowing, striping, defragmentation etc.) and 
all systems do their backup at the same time? (We can use different 
drives of the silo simultaneously)

What is the maximum throughput of the FDDI-connection for backup, 
assuming, 
	- only one of the 6420 is sending backup-data and the 
	  9000/210 is receiving it and 
	- no other bottleneck (discs etc.) exists?
	- no other traffic exists on the FDDI

What happens, when all systems are sending simultaneously?

Klaus