Why is RAID 1+0 better than RAID 0+1?
 

Why is RAID 1+0 better than RAID 0+1? Anyone has any idea !!

Suppose that we have 20 disks to form the RAID 1+0 or RAID 0+1 array of 20 disks.

a) If we chose to do RAID 1+0 (RAID 1 first and then RAID 0), then we would divide those 20 disks into 10 sets of two. Then we would turn each set into a RAID 1 array and then stripe it across the 10 mirrored sets.

b) If on the other hand, we choose to do RAID 0+1 (i.e. RAID 0 first and then RAID 1), we would divide the 20 disks into 2 sets of 10 each. Then, we would turn each set into a RAID 0 array containing 10 disks each and then we would mirror those two arrays.

But then the question is what is the difference from a technical point of view?
I think that is what the TS is looking for; whats the impact; speed difference?

I can't speak for the performance side, but your redundancy kinda goes out the window if your applying a RAID1 to 2x RAID0 arrays.
In a RAID0+1, if a single drive fails in either of the two RAID0's the entire RAID0 should be dropped from the RAID1 as degraded because it can't match it's pair. Technically this only offers single drive redundancy no matter your side.
In a RAID1+0, it's conditional. If a single drive fails, as long as it's RAID1 partner doesn't fail you can still maintain the array through further failures in other pairs.

So as I understand it, RAID 0 isn't really true RAID, one disk fails, you're down. So if you did a RAID 0 + 1...one disk goes down, you're screwed.

I'm be no means an expert, but why would anyone want to do RAID01 or RAID 0. We try to convince ppl not to do RAID 0. Fortunately it's not a question that is asked too often.

Why is RAID 1+0 better than RAID 0+1?
 

Applications requiring both high performance and reliability and willing to sacrifice capacity to get them. This includes enterprise servers, moderate-sized database systems and the like at the high end, but also individuals using larger IDE/ATA hard disks on the low end. Often used in place of RAID 1 or RAID 5 by those requiring higher performance; may be used instead of RAID 1 for applications requiring more capacity.