Howto mdadm¶

have a look at: https://wiki.kobol.io/mdadm/
and also at: http://davidlu1001.github.io/2014/04/14/Linux-quick-guide-for-software-RAID/

or

## var
md=/dev/md0
pd1=/dev/hdc1   ## phys-Disk (Partition)
pd2=/dev/hda3   ## phys-Disk
mnt=/mnt/tmp    ## mount-dir test
mdconf=/etc/mdadm/mdadm.conf
fstab=/etc/fstab
backupdir=/mnt/space ## f. backup $pd1

## check variables
ls -l $md $pd1 $pd2
## pd sollten annaehernd gleiche Groesse haben.
## wichtig:  pd1 <= pd2
fdisk -l | egrep "$pd1|$pd2" 
df -k $backupdir

## backup
dd if=$pd1 | gzip -c > $backupdir/$pd1.dd.gz-`date +%y%m%d`

## create RAID1
mdadm --create $md --level=1 --raid-devices=2 $pd1 missing
cat /proc/mdstat
## add 2. pd
mdadm $md -a $pd2

## create/restore fs (optional)
# gunzip -c $backupdir/$pd1.dd.gz-`date +%y%m%d` | dd of=$md
# mkfs.ext3 $md

## check
cat /proc/mdstat
mdadm --detail --scan
mount -r $md $mnt
ls -l $mnt/
umount $mnt
dd if=$pd1 bs=1k count=2 | hexdump -C
dd if=$pd2 bs=1k count=2 | hexdump -C

## change konfig
ls -la $mdconf
cp -p $mdconf $mdconf.old
[ `grep DEVICE $mdconf | wc -l` -eq 0 ] && echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > $mdconf
#mdadm --detail --scan >> $mdconf
echo "ARRAY $md level=raid1 num-devices=2 devices=$pd1,$pd2" >> $mdconf
more $mdconf

## test stop/start
mdadm -S $md
cat /proc/mdstat
mdadm -A -s -a  ## /etc/init.d/mdadm-raid start
cat /proc/mdstat

## change konfig (final)
cp -p $fstab $fstab.old
cat $fstab.old | sed "s:$pd1:$md:" > $fstab
diff $fstab.old $fstab

change harddrive¶

https://wiki.hetzner.de/index.php/Festplattenaustausch_im_Software-RAID