split backplane on PowerEdge 2650: win or no?

Steve_Boley@Dell.com Steve_Boley at Dell.com
Fri May 21 18:16:01 CDT 2004

The bplane has 2 68pin scsi sockets on it regardless if
it is split or unsplit.  You cannot connect both connectors
and split it without the daughtercard and will give errors
at post if tried.  The connectors are labeled channel a and
channel b on the bplane.  Channel a and no daughtercard and 
7899 channel a on motherboard is 1x5 bplane and channel a on
bplane with daughter card attached to 7899 channel a is a 1x2
bplane and channel b attached to channel b of 7899 is 1x3 bplane.

The daughter card has a slot over the top of the hard drive bays
where it locks into the bplane and enables the scsi controller
in the bplane to split into 2 separate u160 channels.

Hope this helps clear some of the confusion here.

The ROMB (raid on motherboard0 is a actuator chip and dimm that
plugs into the motherboard.  The raid processor and the same 7899
controllers are then enabled to become a raid controller and
the raid processor and logic are embedded in all 2650 motherboards
and in doing this embedding, drove down the overall purchasing
cost for hware raid to the masses.  There are problems with imaging
linux and having multiple channels nonraid so the split bplane 
is not offered with factory install.  A split backplane without
raid was supposed to be made available as long as no os option was
configured, but I don't know if that was ever done.  If you want
to do the sware raid just order without the raid and then add the
2nd cable and the daughtercard and all will be fine.

-----Original Message-----
From: linux-poweredge-admin at dell.com
[mailto:linux-poweredge-admin at dell.com] On Behalf Of James Ralston
Sent: Friday, May 21, 2004 5:52 PM
To: linux-poweredge at dell.com
Subject: RE: split backplane on PowerEdge 2650: win or no?

On 2004-05-21 at 16:45:51-05 Jason_Mick at Dell.com wrote:

> You can either use the internal channels of the ROMB or an addin PCI 
> RAID card to attach to a split backplane.  The ROMB will be cableless 
> design

If I am reading this correctly, since I am using only the onboard SCSI
controllers (no onboard RAID; no other add-in SCSI and/or RAID cards),
simply installing the SCSI backplane daughter card will split the
backplane; no additional cables are required.

On 2004-05-21 at 16:58:33-05 Steve_Boley at Dell.com wrote:

> Can purchase daughtercard and 2nd scsi cable from spare parts and run 
> split bplane with sware raid.
> J0661 is the cable
> 3D735 is the daughtercard
> With the daughter card inserted it will automatically split when you 
> attach the 2nd cable to it.

Attach the second cable *where*?  According to figure 4-23 here:


...the SCSI backplane daughter card has no other connectors on it.
And the first bullet point of instruction #5 says "If a RAID controller
card is not installed, no cables are required to use either the onboard
SCSI controller or optional integrated RAID controller in either a 1 x 5
or 2/3 split configuration."

> This will offload the commands to 2 of the drives to a separate 
> controller so it will help but I'm not sure how much and would really 
> show benefit under load.  The 7899s are on 64bit 66mhz bus of it's own

> so the prev statement of 33 was incorrect so it definitely would be to

> your advantage to split the controllers.

Thanks for the correction...


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