Logical Volume Manager. An Introduction

Logical Volume Manager
An Introduction

Logical Volume Manager What is?
LVM (Logical Volume Manager) allows to manage disks in a different way: creates one or more virtual disks with virtual partitions, from physical partitions
No limited by physical disk

Logical Volume Manager Concepts
Physical Volume (PV) : physical partition from real disk
Volume Group (VG) : like a virtual disk
Logical Volume (LV) : a partition in a Volume Group
Physical Extent (PE) : like a 'cluster' in PV
Logical Extent (LE) : like a 'cluster' in LV

Logical Volume Manager Concepts
Create one or more VG from one or more PV, and then create LVs in each VG
VG /dev/sda1 /dev/vg/lv1 /dev/sda2 /dev/vg/lv2 /dev/vg/lv3

Logical Volume Manager PVs
pvcreate: creates a PV
pvremove: removes a PV
pvdisplay: shows information about a PV
pvscan: scan all PVs in the system
pvck: check a PV for errors
(1) Create one or more partitions with fdisk, with type LVM (2) pvcreate /dev/<partition>

Logical Volume Manager VGs
vgcreate: creates a VG
vgremove: removes a VG
vgextend: extend a VG with more PVs
vgreduce: drops PVs from a VG
vgdisplay: shows info about VG
vgscan: scan for all VGs in system
vgchange: change VG properties
vgck, vgexport, vgmerge, vgsplit, vgrename

Logical Volume Manager VGs (1) Create one or more partitions with fdisk, with type LVM (2) pvcreate /dev/sda1 (3) pvcreate /dev/hdb2 (4) pvcreate /dev/hdc3 (5) vgcreate myvg /dev/sda1 /dev/hdb2 /dev/hdc3

Logical Volume Manager LVs
lvcreate: creates a LV
lvremove: removes a LV
lvscan: scan for all LVs in a system
lvdisplay: shows info about a LV
lvrename, lvresize, lvreduce, lvchange

Logical Volume Manager LVs (1) Create a VG (2) lvcreate -L<size> -n <name> <vg> lvcreate -L10G -n mylv myvg It creates /dev/myvg/mylv (a link to /dev/mapper/myvg-mylv ) mkfs.ext3 /dev/myvg/mylv

Logical Volume Manager Snapshots
A snapshot is an image of a LV
Created instantly
Read-only / read-write (LVM2)
lvcreate -s -L<size> -n <name> <lv> RW: lvcreate -s -L1G -n mylv-snapshot /dev/myvg/mylv RO: lvcreate -s -L1G -n mylv-snapshot -p r /dev/myvg/mylv

Logical Volume Manager Snapshots
Snapshot is like a 'pointer' to the same data in original LV
Each time data in original LV is modified (or in snapshot if it was created as RW), a copy is done previously in exception table
When it becomes full it is automatically disabled

Logical Volume Manager Uses of Snapshots
To test: create snapshots and then use them as the main partitions
If you don't like something, revert to original and drop the snapshots
To backup: use a snapshot to create backups
This way, you can continue to work while backuping is done, without a problem of having an inconsistency
lvcreate -s -L1G -n snaproot /dev/vg/lvroot run-backup.sh /dev/vg/snaproot lvremove -f /dev/vg/snaproot

Logical Volume Manager LVM and other technologies /dev/* /dev/mapper/* /dev/* /dev/* /dev/md0 LUKS RAID

Logical Volume Manager LVM and other technologies /dev/* /dev/mapper/* /dev/* /dev/vg/* /dev/* /dev/* /dev/vg/* LUKS LVM

Logical Volume Manager LVM and other technologies /dev/* /dev/vg/* /dev/vg/* LUKS LVM

Logical Volume Manager LVM and other technologies /dev/vg/* /dev/* /dev/mapper/* LUKS LVM

Logical Volume Manager LVM and other technologies /dev/vg/* /dev/vg/* /dev/* /dev/* LUKS LVM RAID

Logical Volume Manager LVM and other technologies /dev/* /dev/* /dev/* /dev/vg1/* /dev/* /dev/* /dev/* /dev/vg2/* /dev/vg3/* /dev/vg3/* LUKS LUKS LVM LVM LVM

Logical Volume Manager My Laptop /dev/sdaA tmp home swap sbox root var music /dev/sdaB /dev/sdaC LUKS VG-CRYPT VG-UNCRYPT

Logical Volume Manager The End That's all, folks!

Logical Volume Manager. An Introduction

by Juan A. Suárez Romero on Feb 11, 2010

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