How can you verify SCSI performance?

[vash]

I have a couple of Quantum Atlas 10K 9WLS drives and am wondering if they are actually Ultra2Wide or just UltraWide drives. They are connected to the Ultra2 controller, but when I boot Linux, it says only 40mb/sec transfer rate, when I believe it should be 80.

Quantum/Maxtor don't have much on their website in terms of specs, etc, so I come to you, the fine forum members for some more information. Labeled on the drives are references to Ultra160, so I assume these drives could do Ultra2.

vash

 

[Peter]

For U2W and above, you need to have LVD (Low Voltage Differential) cabling and termination. If you don't, or if one of the devices in the chain is UW or below, everything will fall back to SE (Single Ended) operation with a maximum speed of 40 MB/s on a wide cable.

You also need to make sure your SCSI adapter is configured to actually do U2W. What is it? Adaptec? LSI? Tekram? Someone else's? Whatever it is, enter its configuration menu, and make sure the channel isn't manually limited to SE operation.

regards, Peter

 

[vash]

Originally posted by: Peter
For U2W and above, you need to have LVD (Low Voltage Differential) cabling and termination. If you don't, or if one of the devices in the chain is UW or below, everything will fall back to SE (Single Ended) operation with a maximum speed of 40 MB/s on a wide cable.

You also need to make sure your SCSI adapter is configured to actually do U2W. What is it? Adaptec? LSI? Tekram? Someone else's? Whatever it is, enter its configuration menu, and make sure the channel isn't manually limited to SE operation.

The card is an Adaptec 2940U2W. I'll go back into the SCSI BIOS and check to see if SE is on/off. If its on, I'll make sure to leave it off. When the Adaptec boots, it shows the Quantum Atlas drives as Ultra2-SE. I'm assuming the SE is on.

vash

 

[vash]

Here's a bit more information about the disk subsystem:

Adaptec 2940U2W:
SCSI 0: IBM 4gig UW drive on UW channel
SCSI 4: Quantum Atlas 10K 9WLS on U2W/LVD channel
SCSI 6: Quantum Atlas 10K 9WLS on U2W/LVD channel

The drives are pretty much using all default jumpers (SCSI 0 is terminated, the other two aren't terminated, nor do they have any other jumpers enabled). When the devices boot, it shows SCSI0 as Fast-SE, SCSI4/6 as ULTRA2-SE. When I take off the IBM drive and leave only the two Quantum drives, it still says U2W-SE when the system boots and Linux sees the drives as 40Mb/sec transfer.

When you talk about the cable and terminator, I do have a cable terminator and I believe I bought the cable that will support up to 160Mb/sec transfer (bought it in Japan last year, I'm 99% positive it had a label with U160 on it). Maybe I must have a LVD cable, vs a standard cable, to get 80Mb/sec, but what specific setting in the BIOS should I be looking at?

vash

 

[Peter]

See, it says Single Ended everywhere. You need to have an LVD cable (identified by looking funny, they have twisted pair wiring) with LVD termination on the far end.

regards, Peter

 

[vash]

Originally posted by: Peter
See, it says Single Ended everywhere. You need to have an LVD cable (identified by looking funny, they have twisted pair wiring) with LVD termination on the far end.

regards, Peter

Guess I'm gonna have to buy that funny cable for my system, otherwise I'll never break the 40Mb/s barrier. Hope I can get a cable today and hopefully I should see a decrease with load times, etc.

vash

 

[Peter]

You won't. That old Atlas 10K series drive doesn't get near 40 MB/s in linear throughput. Only when both drives are accessed simultaneously will you benefit from the bus bandwidth increase.

regards, Peter