question about PCI/PCI-64/PCI-X bus sharing

question about PCI/PCI-64/PCI-X bus sharing

Post by Ben Hanso » Wed, 07 Dec 2005 22:37:34

I am getting a new motherboard that has an integrated PCI-X Ultra320
controller built in (Adaptec 7902). Unfortunately the version of the Adaptec
controller used in this mobo is not the version that natively supports RAID,
so I am looking into a zero-channel RAID card to provide that feature.

The motherboard doesn't have PCI-X slots but it does have two PCI 64-bit x
66 MHz slots. Companies like Adaptec that sell zero-channel RAID solutions
say that this won't be a bottleneck to the SCSI and RAID performance, but
how can that be? If the controller itself is PCI-X, then when it accesses
the zero-channel device for RAID operations, won't that slower 64 x 66 bus
slow down the whole process?

For that matter is this setup any better (or different performance-wise)
than just bypassing the onboard SCSI controller altogether and getting a 64
x 66 Ultra320 controller that has integrated RAID and just using that

My last question is, the mobo also has 2 normal PCI slots (32 x 33). Are
these a separate bus from the 64 x 66 slots? I want to install a cheap PCI
vid card in the normal PCI slot but if the bus is shared that will destroy
my 64 x 66 device performance, right?


question about PCI/PCI-64/PCI-X bus sharing

Post by Eric Gisi » Thu, 08 Dec 2005 02:19:33

Your system has independent PCI 32/33 and PCI 64/66 (bit/Mhz) buses.
The PCI-X Adaptec is compatible with the latter, and is not a bottleneck.

I would test the OS RAID 5 performance first, and use that
as a basis for evaluating SCSI RAID cards. Some are very poor.


question about PCI/PCI-64/PCI-X bus sharing

Post by Folkert Ri » Thu, 08 Dec 2005 03:44:49

The real question is, is your MoBo Zero Channel Raid compatible.

"The chip features a 66 MHz, 64-bit PCI interface and a 133 MHz, 64-bit PCI-X interface".

Sounds unlikely. More likely it isn't implemented in the BIOS.

AFAIK, that needs a specially designed MoBo. Is your's?

And likely does not have PCI-X either.

The same bus that the Adaptec chip is likely connected to.

It's not. Only if connected to a PCI-X bus.

64x66 = 533 MB/s minus overhead
2*U320 = 640 MB/s minus overhead
SCSI's overhead is bigger than PCI's, that narrows the gap.
And you'll only go into that territory if your devices actually need all that bandwidth.

Read the specs?
If they were to be on the same bus they likely be 32x66, not 32x33.

In your 64 x 66 bus slots, yes.

question about PCI/PCI-64/PCI-X bus sharing

Post by Ben Hanso » Thu, 08 Dec 2005 03:55:21

Thanks Eric. I know it is compatible, but doesn't the slower bus speed of
the 64 x 66 slot where the zero-channel card is plugged in cause a
bottleneck when the controller itself is running at 64 x 133? Or am I not
understanding how the integrated controller and the zero-channel card in the
slot interact with one another?


question about PCI/PCI-64/PCI-X bus sharing

Post by Ben Hanso » Thu, 08 Dec 2005 22:43:28

Hey, yeah it is ZCR-compatible...the mobo is a Supermicro P4SC8 and they say
that it works with the Adaptec 2010S just fine for ZCR support. Your point
below about it not being in the ASIC where the RAID is limited but in the
BIOS is probably true. I asked Adaptec if there is a way for me to "unlock"
this function but of course they said no.

My application is a 4 disk RAID 0 array using 4 Ultra320 15K drives so I
*hope* that the performance using the onboard 7902 Ultra320 ASIC combined
with the 2010S ZCR will be good. Since there aren't any parity calculations
I don't think there will be any problems using this ZCR card or with it
hitting my host processor or anything.


question about PCI/PCI-64/PCI-X bus sharing

Post by Folkert Ri » Fri, 09 Dec 2005 01:01:49

A bit difficult to unlock code that isn't there.
I think the 7902's specialty is in RAID1, not RAID0.
And it still needs some configuration code, even if the
mirroring is done in the chip itself.

Then search google first before you buy. The busses are not the bottleneck.
It's not the first time that Adaptec had problems with their drivers.


The way I look at it, it will only supply the RAID boot code that
is missing in the MoBo bios. Sounds like an expensive solution.
Have you looked at other MoBos?