# lvm.

Glossary:
* *pv*: physical device (e.g. `/dev/md0` or `/dev/sda1`)
* *vg*: volume group (consists of 1 or more *pv*s, contains *lv*s); 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

# cache volume.
TODO: copy from:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/logical_volume_manager_administration/lvm_cache_volume_creation