Lapohos Tibor wrote:

[...]

quoted

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should I create all the partitions first and build
them into so many /dev/md[01234] devices separately maybe?

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I could tell you what seems to be a reasonable setup IMO:
200Mb --> {sda1,sdb1} --> md1 --> RAID1 --> use as /boot
5Gb   --> {sda2,sdb2} --> md2 --> RAID1 --> use as /
...

....and that's exactly what is also on my list, and your suggestion
enforces my thoughts, thanks. Nevertheless, it still does not explain to
me whether multiple md devices with more underlying disk partitions or
more md partitions with fewer underlying disk partitions are the way to
go. To be absolutely clear, is the

/dev/sd[ab]1 => /dev/md0 => /dev/md0p[123...] [RAID1]
/dev/sd[ab]2 => /dev/md1 => /dev/md1p[123...] [RAID0]

I never meant to say to re-partition the md device!!
Why is that needed in a small 200 MByte partition?
I really like the a KISS approach.
 

or the

/dev/sd[ab][123...] => /dev/md[012...] [RAID1,RAID0]

setup the most stable, efficient and robust solution? The way I see it,
there shall be a difference somewhere, somehow, right? About the first
one, thanks to Michael E. pointing it out, we already know that one has to
take care about choosing the patritions.

I can't say what differences or efficiency is there, but it doesn't work!!
So, what does it matter?
Boot your system with the SIMPLE two RAID I stated above, and then, play as 
you wish with as many raid levels and sub-partitions as you want with the 
*rest* of the disks.
 

Furthermore, I think that the gain in speed of RAID0 would start vanishing
if disk access is required on the RAID1 side all at the same time.

In fact, the whole system's efficiency would degrade. The only way out
would be to use 4 disks as

/dev/sd[ab]1 => /dev/md0 => /dev/md0p[123...] [RAID1]
/dev/sd[cd]1 => /dev/md1 => /dev/md1p[123...] [RAID0]

Right? Keep in mind that I am not after what RAID10 can offer. I can
afford giving up the data safety on the RAID0 side in exchange for speed.

Yes, right. Do you have four disks?

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Having only two disks means to use only RAID1. RAID0 is too
risky IMO as any disk failure means a complete loss of data.

I will be developing a numerical electromagnetics code, that will do quite
some number crunching and dumping with 4xTesla C1060 GPUs. I will need the
RAID0 for that purpose, for a scratch space, if you will. So it is a must
have for me.

I was just warning about a possible loss of data, if that is not an issue in 
your system, do set up as many RAID0 as you need.

-- 
Antonio Perez