David Brownlee wrote:
> 	Another option might be to make two of them into a RAID1 set,
> 	with the third as a hotspare, and then have a nightly script
> 	to mount the fourth and rsync across onto it... to save you
> 	from the 'oops, just deleted that' case...

That will only give 3 GB of space though, not the 6GB Henry requested.

There are two configs that give you what you want. 3 disk RAID 5 + hot spare,
or 2 * 2 disk RAID1s, striped together in a RAID0.

In the first case, you have an exposure from the time when the first disk
fails, until the completion of the reconstruction on to the hot space component.

In the second case, you have immediate coverage against a failure of
either disk in the other RAID 1, but no coverage against failure of the
second disk in the same RAID1, until you replace the failed disk
manually.

What's 'safest' depends on which failure mode concerns you more.

As for 'channels', the best performance is clearly with each drive on
its own channel.  That's also the safest, on the off chance that a
channel's controller dies (potentially in a way that takes the drives on
that channel with it, permanently).

--
David Maxwell, david@vex.net|david@maxwell.net --> Although some of you out
there might find a microwave oven controlled by a Unix system an attractive
idea, controlling a microwave oven is easily accomplished with the smallest
of microcontrollers. - Russ Hersch - (Microcontroller primer and FAQ)