split backplane on PowerEdge 2650: win or no?

Eric Swenson eric at reaction-eng.com
Wed May 26 18:13:01 CDT 2004


I'm not sure about the PE2650, but I can definitely testify that the
split backplane with a non-perc, non-raid card works great on a PE4600. 
I have one side connected up to a Perc3DI running RAID1 for /, and the
other side connected to an Adaptec 39160 on a PCI-X slot, with 4 36GB
U320 15K rpm drives.  Each pair of U320 drives is mirrored together with
software raid, and then each mirror is striped  together.  I get a
sustained 140 Megabytes/sec to that array, which is about 10x as fast as
my Perc3/DI mirror.

Eric

On Fri, 2004-05-21 at 17:15, Steve_Boley at Dell.com wrote:
> 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.
> Steve
> 
> -----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:
> 
> http://support.jp.dell.com/docs/systems/pe2650/en/sm/remove.htm#1047294
> 
> ..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...
> 
> James
> 
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