Date: Wed, 29 Oct 2003 07:47:17 +0000 From: Mark Benson <[EMAIL PROTECTED]>
On Wednesday, October 29, 2003, at 06:00 AM, Jeff Walther wrote:
assuming it is not a U2W drive which does not have on-board termination.
U160 and U320 drives don't either for the record.
<grin> Yes, I'm so far behind the times, I forgot about the later drives....
And before you ask I have a pair of U160 Cheetahs in my 840av (I know I'm mad).
Are they on a Jackhammer or just on the built-in? On the built-in would be kind of mad, in terms of real performance of drive vs. maximum speed of SCSI bus, but there's no functional reason not to do it. And you can get the larger capacities. :-)
These complications of termination are why I strongly recommend against folks using adapted drives,
It's not a bad idea at all, it just requires a lot of 'try it and see'. Isn't it recognised that man learns best from his/her own mistakes?
It depends on the audience. My default recommendation is against it, as the lowest common denominator is a person who wants to configure things once, following clear instructions, and not too many of those, and have it work. Many folks don't want to or lack the time or patience to really pay attention to a detailed set of instructions or decision tree for trouble shooting. Those folks should avoid adapting drives, especially because, with SCSI, one doesn't always get a clear indicator of failure when one configures it wrong.
Other folks are willing to/love to tinker and experiment and read detailed explanations. For those folks, adapting drives can be an educational (about SCSI and troubleshooting) experience.
And of course, there are people somewhere in between. So it's difficult to know exactly what advice to give. That's why my default is against it, with the caveat, "If you know what you're doing". If one actually knows what one is doing, then he's just reading my explanation for entertainment anyway. If one wants to learn, he probably won't let that stop him, because there's the caveat and he thinks, but I can learn...
To make things worse, SCSI voodoo, as its called, happens because sometimes (often) SCSI will appear to work even when you configure things incorrectly. This can lead to unnoticed corruption of your devices
Corruption? I never knew that was possible in a Democracy *AHEM* I mean on a SCSI bus.
This is a topic on which I am uncertain. I know that system crashes can lead to SCSI device corruption and I've seen that. I've heard repeatedly that poorly configured SCSI busses can lead to corruption. But I have become dubious about many of the things I've heard, even if I used to read them in MacUser and MacWorld.
I'm not sure I've ever seen SCSI corruption from a poorly configured bus, and I thought that the SCSI devices do a CRC check on data or some such. A CRC check should prevent corruption (most of the time) in a poorly configured SCSI bus, while slowing performance. However, I'm just not certain. I guess I should hike over to that <http://www.scsifaq.org> site that I keep recommending.
That's happened before. It's usually when I plug in a CD drive to re-install the OS.I have a 512MB hard disk the that won't work woth any other devices on the bus on an LC475 (tried in 3 machines) but *will* in an LCIII, odd or what??
That is odd. I am assuming that you have all the SCSI termination angles nailed down. Have you checked the sector size jumper on the CDROM mechanism, assuming it has one. For Macs it should be set to 512, but some CDROMs (especially in Umax machines) were shipped with the sector size jumper set to 1024. If you have a stock Apple external CDROM, this is an unlikely problem, but if it's second hand or something, who knows who's fiddled with the internal jumpers.
Of course, it could just be that your 512 MB drive has a fairly benign defect...
Jeff Walther
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