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Just received a new 1U server - a Dell Poweredge r410.

There are four hot-swap drive trays, which can accommodate either SAS or SATA drives.

However, the odd thing is, instead of a single SFF8087 connector connecting the SAS HBA to the four-drive backplane, there is a SFF8087 cable that splits into two, and connects to the backplane in two places.

This makes no sense - a single SFF8087 cable is capable of supporting four drives, and there are only four drive slots, so ... a plain old SFF8087 cable would be sufficient to connect the SAS HBA to the backplane.

So why split SFF8087 into two, with SFF8087 on each of the other (split) ends ?

The reason this is important is because I do not intend to use the Dell HBA ... I have added my own 4-port 3ware 9650SE card to the system, which also has a SFF8087 port on it. The trouble is two-fold:

  • The dell provided split SFF8087 cable is just short enough so that it cannot be connected to an add-in card

  • there is no such thing as a split SFF8087 cable for sale anywhere. 3ware doesn't make them, adaptec doesn't make them, they're not on amazon, etc. And this makes sense, of course, since there is no reason for that cable to exist - a single SFF8087 can handle all four drives.

So ... why did they do this ?

I am hoping the answer has something to do with unified vs. split drive arrangements, and that somehow this lets you tie one controller to half of the drives and another controller to the other half of the drives and that is why two SFF8087 connectors are on the backplane ... this would also suggest that if I had a plain old SFF8087 cable lying around, I could connect the 3ware directly to the first backplane port and I would see all four drives...

I'll know in a day or so when one arrives in the mail ...

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Doesn't the manual tell you anything about it? –  John Gardeniers Mar 4 '10 at 21:54
    
The answer is probably in dell.com/downloads/global/products/pedge/en/… –  pehrs Mar 4 '10 at 22:27
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2 Answers 2

Almost certainly it's because that backplane is an evolution, rather than a new design of, the old ATA backplane that could only support two drives per channel. I work very closely with HP's server designers and whilst they're always coming up with long lists of great new tech and optimisations they could implement they're actually quite limited in how quickly they can introduce new aspects to their designs. I know it sounds stupid but I really wouldn't put it past their controllers to somehow only support a master/slave system over a much more capable SAS/SATA cable spec. Hope this helps and I'm more than happy for someone to put me right but chances are it's just that dull/old-school :)

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I don't talk to many Dell Server designer, but if you look at the Tech Guidebook, pg 22 Figure 27 each connector only controls two SAS drives, which seems to support your theory. linky: dell.com/downloads/global/products/pedge/en/… –  Zypher Mar 4 '10 at 22:31
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This is the cable that will allow you to connect a third party 6gps pciE raid controller to the Poweredge R410/R415/710 with the "hot swap" drive back plane.

PERC H700i Controller to R710 Backplane Cable - 22in / 56cm - Brand New

http://discountechnology.com/PERC-H700i-to-R710-SAS-Backplane-Cable

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