Re: (OT) Storage (8*IDE HDs) any experiences?
On Monday 30 April 2001 00:04, Hamish Moffatt wrote:
> On Sun, Apr 29, 2001 at 10:14:35AM +0200, Russell Coker wrote:
> > In a regular setup the IDE controller and the drive get power from the
> > same source. So if the signals on the cable have more current going one
> > way than the other then the difference will be made up on the 0V line on
> > the PSU. If you have separate PSU's then the difference will go through
> > other lines of the data cable.
>
> I don't see why. Nor is this any different to any external drives.
> You have a hefty ground connection between the power supplies anyway
> (the mains, plus the metal case acting as ground).
External drives generally don't use an ATA interface! I am not confidant of
the main earth acting as a suitable earth for the DC power.
On Monday 30 April 2001 01:01, Brian May wrote:
> 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.
There was a presentation at a Linux Users of Victoria meeting some years ago
about doing hot-swap IDE hard drives with cheap standard hardware. My
recollection is that the power lines of the hard drive had to be connected in
a particular order...
On Monday 30 April 2001 16:11, PiotR wrote:
> A good solution for this might be to connect the first PS's output to the
> other, so the voltage is the same, and there's no massive current flow
> across the data cables.
That's if both PSU's have exactly the same voltage. If one provides a
slightly higher voltage than the other then it will try to power everything
itself (at least until the current drain lowers the output voltage). Also if
two PSUs with different voltages are connected together with insufficient
load then reverse current will flow through the PSU with the lower voltage!
Go to http://www.raidzone.com/ if you want affordable IDE-based RAID
solutions without all this bother.
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