4 Drive raid setup – 2 SSD raid 1 for system setup and 2 HDD another raid 1 to /storage

First setup the ssd with raid 1 and comment the 2 hdd.

Then

Add a software RAID array

In our example scenario, the drives /dev/sda and /dev/sdb are already combined in multiple RAID1 arrays, which hold the operating system:

cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sda3[2] sdb3[1]
      234405504 blocks super 1.2 [2/2] [UU]
      bitmap: 0/2 pages [0KB], 65536KB chunk

md1 : active raid1 sda2[2] sdb2[1]
      523712 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
      33521664 blocks super 1.2 [2/2] [UU]

unused devices: <none>

But we have two more drives (/dev/sdc and /dev/sdd), which we would like to setup as a data storage with RAID1 array as well. Therefore, the RAID array has to be added first:

mdadm --create --verbose /dev/md3 --level=1 --raid-devices=2 /dev/sdc /dev/sdd

The RAID configuration should now look as follows:

cat /proc/mdstat
Personalities : [raid1]
md3 : active raid1 sdc1[0] sdd1[1]
     2095040 blocks super 1.2 [2/2] [UU]
     	[====>................]  resync = 32.7% (418656/2095040) finish=4.2min speed=131219K/sec

md2 : active raid1 sda3[2] sdb3[1]
      234405504 blocks super 1.2 [2/2] [UU]
      bitmap: 0/2 pages [0KB], 65536KB chunk

md1 : active raid1 sda2[2] sdb2[1]
      523712 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
      33521664 blocks super 1.2 [2/2] [UU]

unused devices: <none>

Now the new partition can be formatted (here with EXT4) and mounted:

mkfs.ext4 /dev/md3
mount /dev/md3 /mnt

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