>> 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 ?
>
>having multiple scsi bus's and segreatting the scsi h/w according to
>speed/capabilities, to the different scsi chains, is a very good idea.
>
>That is to say:
>
> all (and only) your LVD devices (regardless of device type) should
> go on one of your SE/LVD chains. If there are _any_ SE devices on that
> chain, then according to specifications, the adapter must drop down
> to SE mode. This will not hurt you so must w/ transfers, as it will
> with cable length (40MB SE cable length is _ALOT_ shorter than 80MB
> LVD cabling :)
>
> all 40MB SE devices should go on a separate scsi chain (probably
> a wide, or ultra adapter, depending upon the devices)
>
> etc, and put all 5mb on their own chain.
>
>the reason is subtle. the scsi bus runs at the speed of teh slowest device.
>putting a slow device on a scsi bus will probably affect the performance of
>the other scsi devices on that scsi bus.
I understand that. I don't even think of it as subtle!
But its not clear from the mobo docs, or from just staring at the mobo
or from adaptecs web site, whether the U2/LVD connector on the mobo
really represents its own "chain" or just a point to branch a U2/LVD
cable from the one single chain thats connecting everything.
Adaptec do mention a second chip which is specifically for providing
a non U2/LVD bus in conjunction with the 7890, but I have no idea if
this mandatory if you want to put, say, a standard 50 pin wide scsi
connector onto the mobo, or if its a special feature that my mobo does
not have. Supermicro make another board that is specifically
advertised as having 2 SCSI busses.
I am just not really clear on the difference between a chain of cable,
a logical chain and a SCSI bus.
>but none of this is really related to your original question about your
>slow scsi performance. your iron's already going as fast as it can.
understood. its pretty dismal. some people have claimed to have gotten
twice this performance from udma drives that cost probably 50% less. phooey.
--p
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