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From: "Steve Bertrand" <iaccounts@ibctech.ca>
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Subject: RE: gmirror on 1 or 2 IDE cables
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> Using gmirror to mirror two identical drives, how much of a 
> performance hit is it to have
> 
> 1.  Both drives on one IDE cable?
> Compared to:
> 2.  One drive primary on one cable and one secondary on the 
> other cable?
> Compared to:
> 3.  Both drives primary but on separate IDE cables?

My understanding that only a single drive on each IDE channel can be
accessed at any one time.

Thus, if you put one drive on one channel, and the other drive on the
second channel, they can be accessed simultaneously. The location on the
cable(s) does not matter, but I've always got accustomed to putting my
disk drives as primary, which FBSD would see them as ad0 and ad2
respectively.

Steve