How to understand if the RAID array is rebuilt correctly?

Question

linux

I tried to test the reassembly of a RAID1 array on CentOS 6.
I acted according to this scheme phpsuxx.blogspot.com/2009/11/linux-raid0.html
The author had three sections, I have two - this is the main difference, but it is not significant here.
Everything seems to be going well, but one moment is confusing.

Before the test, /proc/mdstat looked like this:

Personalities : [raid1] 
md0 : active raid1 sdb1[1] sda1[0]
      255988 blocks super 1.0 [2/2] [UU]
      
md1 : active raid1 sdb2[1] sda2[0]
      312312700 blocks super 1.1 [2/2] [UU]
      bitmap: 0/3 pages [0KB], 65536KB chunk

unused devices: <none>

And after the test:

Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[2]
      255988 blocks super 1.0 [2/2] [UU]
      
md1 : active raid1 sda2[0] sdb2[1]
      312312700 blocks super 1.1 [2/2] [UU]
      bitmap: 1/3 pages [4KB], 65536KB chunk

unused devices: <none>

Those. the main difference is that on the md0 partition, the numbers in square brackets have changed for the sda1 and sdb2 partitions.
For the author of the original instructions, the same thing happens with the third section (md2). What are these numbers in square brackets and how critical is such a mess with them?

Another question - mdadm --detail for the md0 section issues, in particular, "State: clean", and for md1 - "State: active".
Is it normal? The only thing I can assume is that md0 is inactive, because. they booted from it and left it alone, and all the "movement" takes place on md1, which is why it is listed as active (but is it clean - that's the question).

Answer 1

The brackets [2] indicate the disk number in the mdraid array. As I understand it, it has end-to-end incrementation throughout the life of this mdX.

Answer 2

Do not worry.