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MDADM and LVM cheat sheet

mdadm

Glossary:

  • md: multiple devices
command description
cat /proc/mdstat show status of all raids
mdadm --detail /dev/md0 detailed status of raid md0
mdadm --create /dev/md0 -n2 -l1 /dev/sda1 /dev/sdb1 new raid /dev/md0 with 2 disks, raid level 1 on /dev/sda1 and /dev/sda2
mdadm --fail /dev/md0 /dev/sda1 ; mdadm --remove /dev/md0 /dev/sda1 remove /dev/sda1 from /dev/md0
mdadm --add /dev/md0 /dev/sda1 add /dev/sda1 to /dev/md0
mdadm --grow /dev/md0 -n3 use 3 disks in raid /dev/md0 (e.g. add an additional disk, so a damaged drive can be removed later-on)
mdadm --assemble /dev/md0 Assemble /dev/md0 (e.g. when running live system)
mdadm --detail --scan >> /etc/mdadm/mdadm.conf Update list of arrays in /etc/mdadm/mdadm.conf ; you should remove old list by hand first!
mdadm --examine /dev/sda1 What is this disk / partition?
sysctl -w dev.raid.speed_limit_min=10000 Set minimum raid rebuilding speed to 10000 kiB/s (default 1000)
sfdisk -d /dev/sdX | sfdisk /dev/sdY Copy partition table from sdX to sdY (MBR only)
sgdisk /dev/sdX -R /dev/sdY ; sgdisk -G /dev/sdY Copy partition table from sdX to sdY (GPT)
  • To boot a machine even with a degraded array, modify /etc/initramfs-tools/conf.d/mdadm and run update-initramfs -c -kall (Use with caution!)

lvm

Glossary:

  • pv: physical device (e.g. /dev/md0 or /dev/sda1)
  • vg: volume group (consists of 1 or more pvs, contains lvs); has a name (e.g. lvm)
  • lv: logical volume (has a name which defines its path, e.g. /dev/lvm/root which equals dev/mapper/lvm-root)
command description
pvcreate /dev/md0 initializes /dev/md0 as phys device for a volume group
vgcreate lvm /dev/md0 create volume group lvm with phys device /dev/md0
lvcreate -L30G -nroot lvm ; mkfs.ext4 /dev/lvm/root create logical volume root, sized 30G in volume group lvm; format with ext4
lvextend -L60G -nroot lvm ; resize2fs /dev/lvm/root extend /dev/lvm/root to 60G; also resize file system to new size
pvs, vgs, lvs show short info about pv, vg and lv
pvdisplay, vgdisplay, lvdisplay show long info
pvscan /dev/md0 scan disks for physical volumes (e.g. when running live system)
vgextend lvm /dev/md1 add phys device /dev/md1 to volume group lvm (need pvcreate first!)
pvmove /dev/md0 ; vgreduce lvm /dev/md0 move all logical volumes from /dev/md0 and remove phys device from volume group

Other

create bios grub partition

parted
mklabel gpt
unit s
mkpart bios 64s 2047s
set 1 bios_grub on
mkpart NAME 2048s [end]
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