In my case it stayed as md0 but in theory I think it could assign 
anything, as you say.

On 18-10-04 01:33 PM, Gilbert E. Detillieux wrote:
On 04/10/2018 1:23 PM, Gilles Detillieux wrote:
 Thanks, Scott.

 One of the steps in the tutorial is to save the MD RAID configuration 
 in /etc/mdadm/mdadm.conf. They suggest using "sudo mdadm --detail 
 --scan | sudo tee -a /etc/mdadm/mdadm.conf", which I did. In your 
 approach, that step isn't done. Is this a detail that pvcreate looks 
 after for you, either by adding to that file itself, or saving the 
 setup elsewhere? 
 No, the LVM commands will not affect MD configuration at all. Strictly 
 speaking, the mdadm.conf file (location may vary, depending on distro) 
 isn't necessary.  Without it, the MD arrays will still be detected and 
 assembled at boot time, but you may get different device names 
 assigned to them (e.g. /dev/md127, instead of /dev/md0).

 If you want consistent device names, it's best to have the mdadm.conf 
 file.  (If you're going to use UUID's or logical volume names to refer 
 to your devices, then the actual assigned md device name doesn't matter.)

 Gilbert

 This was the only part of DigitalOcean's procedure that I found to be 
 a bit kludgy. I was surprised that there wasn't something right in 
 mdadm to manage the saving of the configuration more automatically. 
 Adding the fstab entry was as I'd expect for any file system type. 
 Other than that, things were pretty plug-and-play, with no messing 
 around with systemctl or anything like that required. After a reboot, 
 the RAID array was back in action just as it should be.

 On 10/04/2018 10:07 AM, Scott Toderash wrote:
 Here are my notes from the last time I build a Linux RAID on LVM. 
 This was on 16.04LTS

 I think my approach was slightly different. The RAID device is 
 created on the LVM devices.

 1. create partitions of type Linux RAID Autodetect on both disks
 fdisk -l /dev/sdb
 fdisk -l /dev/sdc
 2. create a RAID array called md0 using mdstat
 sudo mdadm --create /dev/md0 --level=mirror --raid-devices=2 
 /dev/sdb1 /dev/sdc1
 3. add the md0 raid device to the LVM pool
 sudo pvcreate /dev/md0
 4. create a volume group called datavg
 sudo vgcreate datavg /dev/md0
 5. create a logical volume called datalv within the volume group
 sudo lvcreate --name datalv --size 1.8T datavg
 6. format the newly created logical volume
 sudo mkfs.ext4 /dev/datavg/datalv
 7. move home files to a temporary location, create a new home and 
 mount the newly formatted device there, copy the original home files 
 to the new device
 sudo mv home home.orig; sudo mkdir home ; sudo chmod 777 home ; sudo 
 mount /dev/mapper/datavg-datalv /home ; sudo cp -a /home.orig/* home
 8. edit fstab for startup config for this disk
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