split backplane on PowerEdge 2650: win or no?

James Ralston qralston+ml.dell-poweredge at andrew.cmu.edu
Fri May 21 15:12:01 CDT 2004

If one is using the on-board Ultra/160 controller on a PowerEdge 2650
system, is there any real-world performance win in running in split
backplane mode?

The onboard Ultra/160 controller seems to sit on its own 33MHz PCI
bus.  The theoretical maximum throughput of 33MHz PCI is 132MB per
second.  The theoretical maximum throughput of Ultra/160 is 80MB per

We have a PowerEdge 2650 with the front drive bays completely
populated: 1 Fujitsu MAP3367 disk (the system disk), and 4 Fujitsu
MAS3367 disks.  The MAS3367's data transfer rate is between 93.1 to
118.2 MB per second.  The front drive bays are not running in split
bus mode; all 5 disks are on channel A of the onboard Ultra/150

It would *seem* that the Ultra/160 bus, not the PCI bus, would be the
performance bottleneck: 2 of the MAS3367 drives bursting at the same
time could saturate the Ultra/160 bus.  However, if I went with a
split backplane configuration (assuming disks 0-2 would be on channel
A, and disks 3-4 would be on channel B), it would help to alleviate
the bottleneck.

This all seems reasonable to me, but it's purely theoretical; there
might be important performance considerations w/respect to the
PowerEdge 2650 hardware of which I'm unaware.

Does anyone who's already been down this path have any salient advice?

>From what I can tell from the PowerEdge 2650 manual, all that's needed
to split the backplane is to install the daughter card; no additional
cables are needed.  Is this correct?

Thanks, and regards,

James Ralston, Information Technology
Software Engineering Institute
Carnegie Mellon University, Pittsburgh, PA, USA

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