Re: (OT) Storage (8*IDE HDs) any experiences?

[Brian May <bam@debian.org>]

>>>>> "Russell" == Russell Coker <russell@coker.com.au> writes:

    Russell> That sounds like a really bad idea to me.

    Russell> In a regular setup the IDE controller and the drive get
    Russell> power from the same source.  So if the signals on the
    Russell> cable have more current going one way than the other then
    Russell> the difference will be made up on the 0V line on the PSU.
    Russell> If you have separate PSU's then the difference will go
    Russell> through other lines of the data cable.  This is something
    Russell> that is likely to be fatal to drives and motherboards.

    Russell> But if you try it please let me know how it works.  ;)

Another thing to watch out for is timing differences. Eg. if you turn
on one power supply before the other. Or if one power supply generates
good power before the other.

I would assume (hope!) the original poster plans to run both power
supplies from the same central switch, in order to minimise problems
here.

Designers of the interface need to take into consideration if it is
going to be used for external devices powered by external power or
internal devices. A number of factors need to be taken into account
ranging from internal delays in the power supply, logic levels, cable
length vs cable quality vs speed of communication vs reliability of
communication, ground loops, etc.

So, while the above might be OK for an SCSI interface for external
devices, I strongly suspect when designing IDE that they made the
assumption it would only be used for the one power supply. Hence I
wouldn't like to try it, unless I didn't care about reliability and/or
potentially wrecking the hard disks. Even if it works today, will it
work tomorrow?
-- 
Brian May <bam@debian.org>