Messages in this thread | | | Date | Fri, 7 Mar 1997 22:47:42 -0600 (CST) | From | Edward Welbon <> | Subject | Re: your mail |
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On Mon, 3 Mar 1997, Richard B. Johnson wrote:
> This is the SCSI driver. No external drives are attached, and the internal > drives are connected with a SHORT cable properly terminated on the far end.
A too short SCSI cable is a no-no. The problem is that a scsi cable is actually a transmission line and the points where devices connects are essentially points of discontinuity which alter the characteristic impedance of the cable. Depending on the impedance of the the drives and the impedance of the cable, you can have *too* *short* a cable. I think that you will generally be safe with one foot between connections on the cable. Less than one foot per connection and the dominating impedance may be that of the drives and not that of the cable. because of this, too short is bad. I certainly would not use less than 6" of cable between connectors (and this only with drives that present not more than 10 picofarads of capacitance at the scsi interface).
If you doubt me, then by all means check out appendix C of the scsi 3 spec. My scsi stuff works f*cking great (I can read and write my md raid at 42 MB/s and I am mounting / on /dev/md0 via initrd). I don't doubt that there are faster controllers, but my adaptech's are dang reliable.
Ed Welbon; welbon@bga.com;
Any sufficiently advanced technology is indistinguishable from linux... Flush bill, choose linux.
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