Re: incredibly poor SCSI performance - why ?

From: Paul Barton-Davis (pbd@Op.Net)
Date: Wed Apr 05 2000 - 08:17:03 EST

Thanks for the very useful reply. A little minor feedback ...

>speeds over 350mbits/sec. One of my IBM drives (one of the newer 18G models)
>moves data @ 19MB/s (it's attached to a 2940UW.)

I have 3 of the IBM 18GB speedstars as well, I should try them
out. But I wasn't aware (unbelievably) of the existence of an internal
transfer rate. Now I know better.

>Taged commands are off, there's a speed killer.

Yes, I have some devices that don't like them, and I've never
reenabled them individually for the disks. I should try this.

>> 10: 1740 1756 IO-APIC-level aic7xxx, RME Digi9652
>And you're sharing an interrupt. That'll burn a little speed.

Yes, I know, its not very nice, and I still haven't found a way to
force it to be otherwise. The AMI BIOS doesn't seem to play along with
my attempt to assign different priorities to the slots.

>Umm, I don't think so... 80MB/s is an LVD speed. You cannot have both LVD
>and non-LVD hardware on the same cable in LVD mode. There doesn't appear to
>be any isolation chip on that MB (and SuperMicro doesn't list one) so it's
>actually _40_MB/s but that doesn't matter for the purposes here -- the bus
>is faster than the drive. Besides, you've got too many devices to fit on a
>proper SE FAST-40 (U2/SE) bus. Again, this is immaterial to speed.

There are 3 SCSI connectors on the motherboard, one U2/LVD-SE, one
regular old wide SCSI and one Ultra SCSI. The disks are the only
things connected to the U2/LVD-SE connector. I got the impression from
the adaptec site that if I set things up this way, I got an isolated
U2/LVD bus. Is this not true ?


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