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

[Ben Hanson]

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
instead?

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?

-Ben

 

[Peter]

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
instead?

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?

What is your motherboard make/model?

 

[Ben Hanson]

Supermicro P4SC8

I needed this one cause my proc at this time is a P4 Prescott (478).

 

[Peter]

Supermicro P4SC8

I needed this one cause my proc at this time is a P4 Prescott (478).

Those two are PCI-X slots (64-bit, 66MHz, 3.3V)

There is no mismatch, so there is no slowdown. This bus is up to 533MB/s.

There is no point in doing that (from bus perspective) but some other
controllers might be simply better.
So you have lots of fast SCSI disks?

Yes, they are on a separate bus.

It is not shared.

 

[Folkert Rienstra]

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

I am getting a new motherboard that has an integrated PCI-X Ultra320
controller built in (Adaptec 7902).

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

Unfortunately the version of the Adaptec controller used in
this mobo is not the version that natively supports RAID,

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

so I am looking into a zero-channel RAID card to provide that feature.

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

The motherboard doesn't have PCI-X slots

And likely does not have PCI-X either.

but it does have two PCI 64-bit x 66 MHz slots.

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

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,

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

then when it accesses the zero-channel device for RAID operations, won't that slower
64 x 66 bus slow down the whole process?

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.

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
instead?

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?

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

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?

In your 64 x 66 bus slots, yes.

 

[Ben Hanson]

Thanks Peter. In my application I have 4 Ultra320 15K drives in a RAID 0
array. So I guess what I was thinking was that although I know the
integrated controller and the zero-channel card/PCI slot are both PCI-X,
that the former is at 133 MHz where the latter is only at 66 MHz. And so it
seemed to me that between the card and the integrated controller was a
bottleneck. Am I just not understanding how the integrated SCSI controller
and the zero-channel RAID card interact with one another?

-Ben

 

[Peter]

Thanks Peter. In my application I have 4 Ultra320 15K drives in a RAID 0

array. So I guess what I was thinking was that although I know the
integrated controller and the zero-channel card/PCI slot are both PCI-X,
that the former is at 133 MHz where the latter is only at 66 MHz. And so it
seemed to me that between the card and the integrated controller was a
bottleneck. Am I just not understanding how the integrated SCSI controller
and the zero-channel RAID card interact with one another?

ZCR card, what card? Supermicro recommends Adaptec 2010S. Is that what you
have? That card is also 64-bit/66MHz PCI. Your MB has 64-bit/66MHz PCI-X
slots.MB chipset (6300ESB) has also 64-bit/66MHz connection to PCI-X.
Bottleneck? Of what sort? What kind of application is yours?