Raid with mdadm

• https://raid.wiki.kernel.org/index.php/A_guide_to_mdadm
• https://wiki.ubuntuusers.de/Software-RAID/
• https://www.thomas-krenn.com/de/wiki/Software_RAID_mit_MDADM_verwalten

Install

By default, mdadm recommends a mail agent (defaulting to exim), so if you don't need one don't install the recommends:

sudo apt install --no-install-recommends mdadm

Show info

cat /proc/mdstat
mdadm --detail /dev/md0

Create raid

https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-16-04#creating-a-raid-1-array

• Use partitions, not whole disks!

• Make sure both disks are excatly the same size (compare sectors with fdisk -l -u sectors /dev/sdX)

apt install mdadm

mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1

Show raid state:

cat /proc/mdstat

Sync will happen in background, /dev/md0 is immediatly usable!

Create degraded raid

Use case: sync old backup data to one disk before adding another disk to complete the array.

https://documentation.suse.com/sles/15-SP1/html/SLES-all/cha-raid-degraded.html

Create a degraded array

mdadm --create /dev/md0 -l 1 -n 2 /dev/sdX1 missing

Then later add second disk:

mdadm /dev/md0 -a /dev/sdY1

Setup raid1 with encrypted LVM

export RAID_DEV='/dev/md0'
export LUKS_NAME='cryptraid'
export VG_NAME=$LUKS_NAME
export LV_NAME='backup'

Partition disk:

parted /dev/sdX mklabel gpt --script
parted /dev/sdX mkpart primary 0% 100% --script

parted /dev/sdY mklabel gpt --script
parted /dev/sdY mkpart primary 0% 100% --script

Create raid1:

mdadm --create $RAID_DEV -l 1 -n 2 /dev/sdX1 /dev/sdY1

Luks-format it:

cryptsetup luksFormat $RAID_DEV
cryptsetup open --type luks $RAID_DEV $LUKS_NAME
cryptsetup status $LUKS_NAME

Create LVM:

pvcreate /dev/mapper/$LUKS_NAME
vgcreate $VG_NAME /dev/mapper/$LUKS_NAME
lvcreate -L 400gb -n $LV_NAME $VG_NAME

mkfs.ext4 -m 0 -L $LV_NAME /dev/${VG_NAME}/${LV_NAME}
mount /dev/${VG_NAME}/${LV_NAME} /mnt

Delete raid1

mdadm --detail /dev/md3
mdadm --stop /dev/md3
mdadm --zero-superblock /dev/sda4
mdadm --zero-superblock /dev/sdb4

Shrink root software raid

http://www.webdesignblog.asia/operating-systems/linux-os/resizeshrink-raid1-filesystemvolumepartition-and-setup-a-lvm-on-the-free-disk-space-created/#sthash.gdUNQpuw.ohySozoz.dpbs

root-part: md2 (sda3 + sdb3)

resize2fs -f /dev/md2 30G

13% mehr als 30G -> 34G 3410241024

mdadm --grow /dev/md2 --size=35651584

15% mehr als 30G -> 35G

Start inactive array

md0 : inactive sda1[0](S) sdb1[2](S)

mdadm --run /dev/md0

md0: active (auto-read-only) raid1 sda1[0] sdb1[2](S)

Re-assemble existing raid

sudo mdadm --assemble --scan

Rebuild

https://www.thomas-krenn.com/de/wiki/Software_RAID_mit_MDADM_verwalten#Rebuild

md0 : active (auto-read-only) raid1 sdb1[0](S) sda1[2]

In this case, sdb1 is unused, spare device. Remove it:

mdadm --manage /dev/md0 -r /dev/sdX1

Partition disk:

parted /dev/sdX mklabel gpt --script
parted /dev/sdX mkpart primary 0% 100% --script

Add disk to array:

mdadm --manage /dev/md0 -a /dev/sdX1