for some reason… did ext3 on RAID1 with two disks (seagate + wd) of different sized (2TB but they (of course) are not exactly 2TB)

watch out: shingled hdd are not good for RAID!

not sure where the problem here was 1) kernel 2) ext3 3) the disks…

have a sufficient sized external USB harddisk ready to save backup data to

# tested on Debian 10, should work on other distros as well

# mount one disk to backup all data from a failed raid1
# (the second wd disk always dropped out of raid)
# (not sure was the problem was 1) kernel (older) 2) hardware 3) ext3)
# checkout this guide on what hardware is raid-able

# what devices are there
## show harddisks and partitions
lsblk -fs
## the more fancy harddisk view
# create mount point
mkdir -p /media/user/md1
# start raid1 with one of the two disks
# (should have identical content)
mdadm --assemble --run /dev/md1 /dev/sde1
# it might also be possible not at all specify the exact partition harddisk to use
# but let mdadm do the auto detecting job
# was tested and worked perfectly fine
mkdir -p /media/user/md0
mkdir -p /media/user/md1
mkdir -p /media/user/md2
mkdir -p /media/user/md3

mdadm --assemble --run /dev/md0
mdadm --assemble --run /dev/md1
mdadm --assemble --run /dev/md2
mdadm --assemble --run /dev/md3

# this is the swap, no need to mount it
mount /dev/md0 /media/user/md0 
mount: /media/user/md0: unknown filesystem type 'swap'.

mount /dev/md1 /media/user/md1
mount /dev/md2 /media/user/md2
mount /dev/md3 /media/user/md3

# checkout what is in the partitions
ls -lah /media/user/md1
# aha! kernels! so it is the boot partition
ls -lah /media/user/md2
# aha! home! this is the main data and root partition
# (if home and root is the same partition)

# run the backup
rsync -r -vv --update --progress /media/user/md1/ /media/user/mount/point/of/external/usb/harddisk

# optional: get more info about the disks	 	 

hdparm -I /dev/sde|grep Model	 	 
 Model Number: ST2000NM0033-9ZM175 	 	 
blockdev --report /dev/sde	 	 
RO RA SSZ BSZ StartSec Size Device	 	 
rw 256 512 4096 0 2000398934016 /dev/sde	 	 

hdparm -I /dev/sdf|grep Model	 	 
 Model Number: WDC WD20EARS-00MVWB0	 	 

blockdev --report /dev/sdf	 	 
RO RA SSZ BSZ StartSec Size Device	 	 
rw 256 512 512 0 2000397852160 /dev/sdf	 	 

# seagate + wd, will it go together? X-D	 	 

# after backup complete
# make sure disks are umounted	 	 

# sync write caches
sync; sync; sync;
# unmount all raid device-partitions
umount /dev/md*
mdadm --stop /dev/md1	 	 
mdadm --remove /dev/md1