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

[Hamish Moffatt <hamish@debian.org>]

On Tue, May 01, 2001 at 11:03:06AM +0200, Russell Coker wrote:
> On Monday 30 April 2001 00:04, Hamish Moffatt wrote:
> > 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.

True, but I don't see this as a big issue.

> 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.

I think it would be better to deliberately turn them on in order, rather
than trying to guess at the same time. Turn the hard drives on first.
They may or may not spin up while the controller is powered off. Then
turn on the main supply.

> 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...

Standard power supplies may have sequencing to switch the supplies on a
known order. That doesn't stop you powering them from different power
supplies though, as the sequencing isn't under motherboard control.

> 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!

Yes, that's a bad idea.


Hamish
-- 
Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>