Just some notes on my current MDADM setup, so I do not forget.
So my current hard drives are:
# lsscsi
[0:0:0:0] disk ATA Samsung SSD 860 1B6Q /dev/sda
[4:0:0:0] disk ATA WDC WD4003FZEX-0 1A01 /dev/sdb
[5:0:0:0] disk ATA WDC WD5000AAKS-0 3B01 /dev/sdc
[5:0:1:0] disk ATA ST2000DM001-1CH1 CC29 /dev/sdd
[10:0:0:0] disk WD Ext HDD 1021 2021 /dev/sde
[11:0:0:0] disk WD Ext HDD 1021 2021 /dev/sdf
The first one is my primary and Operating Systems and all that. Seems obvious.
The second one contains a large partition for my /home on sdb1.
Partition sdc1 of the sdc drive is a simple 500Gb partition containing some odds and ends. Not big enough for the RAID, not fast enough for the operating system.
Starting my raid setup I can do with:
# mdadm --assemble /dev/md127 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdb2
mdadm: /dev/md127 has been started with 4 drives.
Just so you know, it's a simple mirror setup, so I am using 4 drives to mirror a 2 TB partition.
And then I simple mount the damn thing with:
# mount /dev/md127 /mnt/raid/
Then I can watch the status with detail:
mdadm --detail /dev/md127