= bionic verification =
ubuntu@ip-172-30-0-117:~$ sudo mdadm --create /dev/md0 --run --metadata=default --level=0 --raid-devices=4 /dev/xvdb /dev/xvdc /dev/xvdd /dev/xvde
mdadm: array /dev/md0 started.
ubuntu@ip-172-30-0-117:~$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid0 xvde[3] xvdd[2] xvdc[1] xvdb[0]
      29323264 blocks super 1.2 512k chunks
      
unused devices: <none>

## kernel & mdadm upgrade

ubuntu@ip-172-30-0-117:~$ dmesg | grep raid
[    4.086107] md/raid0:md0: cannot assemble multi-zone RAID0 with default_layout setting
[    4.092253] md/raid0: please set raid0.default_layout to 1 or 2
[    4.452725] raid6: avx2x4   gen() 24200 MB/s
[    4.500724] raid6: avx2x4   xor() 15657 MB/s
[    4.548725] raid6: avx2x2   gen() 21010 MB/s
[    4.596724] raid6: avx2x2   xor() 13248 MB/s
[    4.644724] raid6: avx2x1   gen() 18005 MB/s
[    4.692726] raid6: avx2x1   xor() 12606 MB/s
[    4.740726] raid6: sse2x4   gen() 13375 MB/s
[    4.788725] raid6: sse2x4   xor()  8309 MB/s
[    4.836730] raid6: sse2x2   gen() 11042 MB/s
[    4.884725] raid6: sse2x2   xor()  7264 MB/s
[    4.932730] raid6: sse2x1   gen()  9288 MB/s
[    4.980723] raid6: sse2x1   xor()  6578 MB/s
[    4.983827] raid6: using algorithm avx2x4 gen() 24200 MB/s
[    4.987535] raid6: .... xor() 15657 MB/s, rmw enabled
[    4.991018] raid6: using avx2x2 recovery algorithm
ubuntu@ip-172-30-0-117:~$ cat /proc/mdstat
Personalities : [raid0] [linear] [multipath] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : inactive xvdd[2] xvde[3] xvdb[0] xvdc[1]
      29323264 blocks super 1.2
       
unused devices: <none>
ubuntu@ip-172-30-0-117:~$ sudo mdadm --stop /dev/md0
mdadm: stopped /dev/md0
ubuntu@ip-172-30-0-117:~$ sudo mdadm --assemble /dev/md0 -U layout-alternate /dev/xvdb /dev/xvdc /dev/xvdd /dev/xvde
mdadm: /dev/md0 has been started with 4 drives.
ubuntu@ip-172-30-0-117:~$ cat /proc/mdstat
Personalities : [raid0] [linear] [multipath] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid0 xvdb[0] xvde[3] xvdd[2] xvdc[1]
      29323264 blocks super 1.2 512k chunks
      
unused devices: <none>

## reboot
ubuntu@ip-172-30-0-117:~$ dmesg | grep raid
[    3.793154] raid6: avx2x4   gen() 24292 MB/s
[    3.841155] raid6: avx2x4   xor() 15646 MB/s
[    3.889157] raid6: avx2x2   gen() 20570 MB/s
[    3.937155] raid6: avx2x2   xor() 13351 MB/s
[    3.985155] raid6: avx2x1   gen() 18190 MB/s
[    4.033154] raid6: avx2x1   xor() 12469 MB/s
[    4.081153] raid6: sse2x4   gen() 13399 MB/s
[    4.129153] raid6: sse2x4   xor()  8358 MB/s
[    4.177151] raid6: sse2x2   gen() 10984 MB/s
[    4.225157] raid6: sse2x2   xor()  7224 MB/s
[    4.273158] raid6: sse2x1   gen()  9335 MB/s
[    4.321157] raid6: sse2x1   xor()  6578 MB/s
[    4.323567] raid6: using algorithm avx2x4 gen() 24292 MB/s
[    4.326583] raid6: .... xor() 15646 MB/s, rmw enabled
[    4.329350] raid6: using avx2x2 recovery algorithm
ubuntu@ip-172-30-0-117:~$ cat /proc/mdstat
Personalities : [raid0] [linear] [multipath] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid0 xvde[3] xvdb[0] xvdc[1] xvdd[2]
      29323264 blocks super 1.2 512k chunks
      
unused devices: <none>
ubuntu@ip-172-30-0-117:~$ sudo mdadm --stop /dev/md0
mdadm: stopped /dev/md0

ubuntu@ip-172-30-0-117:~$ sudo mdadm --create /dev/md0 --run --metadata=default --level=0 --raid-devices=3 /dev/xvdb /dev/xvdd /dev/xvde
mdadm: /dev/xvdb appears to be part of a raid array:
       level=raid0 devices=4 ctime=Fri Dec  6 22:20:04 2019
mdadm: /dev/xvdd appears to be part of a raid array:
       level=raid0 devices=4 ctime=Fri Dec  6 22:20:04 2019
mdadm: /dev/xvde appears to be part of a raid array:
       level=raid0 devices=4 ctime=Fri Dec  6 22:20:04 2019
mdadm: array /dev/md0 started.
ubuntu@ip-172-30-0-117:~$ sudo mdadm --detail /dev/md0 | grep Layout
            Layout : original