On Mon, 29 Jul 2019 17:27:15 -0300
"Guilherme G. Piccoli" [off-list ref] wrote:

Hi Roman, I don't think this is usual setup. I understand that there are
RAID10 (also known as RAID 0+1) in which we can have like 4 devices, and
they pair in 2 sets of two disks using stripping, then these sets are
paired using mirroring. This is handled by raid10 driver however, so it
won't suffer for this issue.

I don't think it's common or even makes sense to back a raid1 with 2
pure raid0 devices.

It might be not a usual setup, but it is a nice possibility that you get with
MD. If for the moment you don't have drives of the needed size, but have
smaller drives. E.g.:

- had a 2x1TB RAID1;
- one disk fails;
- no 1TB disks at hand;
- but lots of 500GB disks;
- let's make a 2x500GB RAID0 and have that stand in for the missing 1TB
member for the time being;

Or here's for a detailed rationale of a more permanent scenario:
https://louwrentius.com/building-a-raid-6-array-of-mixed-drives.html

-- 
With respect,
Roman