Some help with SCSIing?

[Behemot]

Hi guys,

I finally made my shiny computer complete. Last night I greatly suffered with making all my SCSi drives working, mainly due to I did not have ID jumpers table for settings ID's through the SCA-80 to LVD-68 adapter.

Finally all drives were dected with ID 0, 1 and 6. Now two of them work fine, the last fine is terribly slow. I know SCSi is excellent for burst rate, but I guess sustained transfer rate of less than 3 MB/s is still too low :-)

The adapter is Adaptec 29160 in 32bit PCI, drives are Seagate Cheetah 15k5, 15k3 and 15k5 again. They're connected on third, second and first connector (starting from terminated end of cable).

Any idea where the problem is? I guess it's just cable layout or ID problem? When I connected the 15k5 drives alone('both are identicall) and tested them with controller's read test, both were equally fast in that test.

[Behemot]

Re: Some help with SCSIing?

OK so I've swapped the 15k5 Cheetah's and all drives are now arround 80 MB/s in read. I gues that when I drops to 40 MB/s while I run read test (HD Tune) on two drives, the problem is in PCI throughput?

I expected speeds arround 120 MB/s, hell even 100 MB/s would be fine, but 80 I'll have to look for a PCIe controller sooner than I thought.

[Shodan486]

Re: Some help with SCSIing?

Cabas,

Fuuu, ale od PCI take veci nemozes cakat (In english: Well, you can't expect things like these from the PCI bus).

EVERYTHING you have is OK, all the drives and controller DO support speeds like you mention, but the implementation on the simple PCI bus suxx. The theoretical speed of PCI is 133MB/s, we all know that, but let's just do some little math:

I reckon this is a server based system, so with the audio card excluded, you face a share of bandwith for the LAN (possibly even 2), VGA (not expecting AGP bus), IDE (try switching it off) and some motherboards with two CPUs (mainly P3s) communicate via the PCI bus, so here you have some of the MBs/s lost. Please post us the mobo you're using. Personally I think you reached the top of the PCI possibilities.

[Behemot]

Re: Some help with SCSIing?

No way. Thats AMD 880G system (basicly renamed 780G). Acording to scheme, there is nothing on PCI bus:


I am still not sure whether really the problem is PCI - it is too far from theoretical 133 MB/s and suspiciosly close to nearest slower SCSi speed - 80 MB/s. As it was in asynchronnous mode. Because if I understand SCSi, one of the advantages is the data can flow directly disc-to-disc without going through PCI to somewhere and back? In that case shouldn't it have speeds betwen 100 and 150 MB/s (it's totaly possible, the Cheetah's 15k5 have theoretical disc-to-buffer maximum of 171 MB/s). I tried to copy 1,5GB file between the two disks several times and it sometimes starts realyl fast (hudres of MB/s), sometimes it's slower but usually between 60-100 MB/s average.

I just want to be sure that if I buy that cheapest SCSi PCIe controller (Adaptec 29320LPE) somewhere, I'll get speeds far over 100 MB/s per disk.