Ok I got 2 optical drives on the secondary IDE channel and 1 HDD on the primary IDE channel. I want to add another identical drive as the one I have for backup purposes (no RAIDing in 0 or 1) - what is optimal? Put it as slave on the primary channel along with the other HDD, right?

Doesn't really matter.

You could put it secondary master and make both optical drives slaves, but it could lower CD recording or DVD performance. If you're just using that hard drive as a backup, you really don't need it to be "fast", so yeah, your setup is fine.

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