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LVM Reference

2013-08-11

There are already some LVM tutorials out there and I don’t want to write another one. Most of the time you just need a reference for the most common commands.

create

Physical Volume (PV)

pvcreate /dev/sdb

Volume Group (LV)

vgcreate vg_data /dev/sdb

Logical Volume (LV)

lvcreate –L 10G –n lv_data01 vg_data
mkfs.ext3 /dev/vg_data/lv_data01
mount /dev/vg_data/lv_data01 /data01

Info

pvdisplay 
pvs

vgdisplay vg_data
vgs

lvdisplay lv_data
lvs

Extend LV

Add a disk and use it

vgcreate vg_data /dev/sdc
vgextend vg_data /dev/sdc
lvextend –L+2G /dev/vg_data/lv_data01
resize2fs –p /dev/vg_data/lv_data01

Extent to maximal size:

lvextend -l+100%FREE /dev/vg_data/lv_data01

Shrink LV

umount /data01
e2fsck –f /dev/vg_data/lv_data01
resize2fs –p /dev/vg_data/lv_data01 19G
lvreduce –L20G /dev/vg_data/lv_data01
mount /dev/vg_data/lv_data01 /data01
resize2fs –p /dev/vg_data/lv_data01

Rename

VG

vgrename vg_data vg_newname

LV

lvrename /dev/vg_data/lv_data01 /dev/vg_data/lv_new_name01
  or
lvrename vg_data lv_data01 lv_new_name01

Remove a disk

pvmove –v /dev/sdc
vgreduce vg_data /dev/sdc
pvremove /dev/sdc

Delete

LV

umount /dev/vg_data/lv_data01
lvremove /dev/vg_data/lv_data01

VG

vgremove vg_data

PV

pvremove /dev/sdc1

LVM Advanced

Striped LV

lvcreate –L 10G –i2 –I64 –n lv_data02 vg_data
-L 10G = LV size
-i2    = use two disks
-I64   = chunk size 64kb

A striped LV is organizing the data into chunk and uses more disks to increase performances. It is similar to Raid0
VG must have PVs on different hardware. It makes no sense to put sda1 and sda2 into a VG and stripe the LV.

example:

# pvcreate /dev/sdb
# pvcreate /dev/sdc
# vgcreate vg_data /dev/sdb /dev/sdc
# lvcreate -L 1G -n lv_data_default vg_data 
# pvs
  PV         VG      Fmt  Attr PSize PFree   
  /dev/sdb   vg_data lvm2 a-   2.00g 1020.00m
  /dev/sdc   vg_data lvm2 a-   2.00g    2.00g
# lvcreate -L 1G -i2 -I64 -n lv_data_stripe vg_data
# pvs
  PV         VG      Fmt  Attr PSize PFree  
  /dev/sdb   vg_data lvm2 a-   2.00g 508.00m
  /dev/sdc   vg_data lvm2 a-   2.00g   1.50g

Mirror

You can also mirror you data for redundancy reasons which is similar to Raid1

lvcreate -L 500M -m1 --mirrorlog core -n lv_data03 vg_data
-m1              = one aditional copy = written two times on the disk
--mirrorlog core = log only in memory = rebuild after a reboot (otherwise you need three PVs in the VG, 2 for the data and 1 for the log)

example 1 – (two disks, mirrorlog stored in RAM):

# lvcreate -L 500M -m1 --mirrorlog core -n lv_data01_mirror vg_data
  Logical volume "lv_data01_mirror" created
# pvs
  PV         VG      Fmt  Attr PSize PFree
  /dev/sdb   vg_data lvm2 a-   2.00g 1.51g
  /dev/sdc   vg_data lvm2 a-   2.00g 1.51g
# mkfs.ext4 /dev/vg_data/lv_data01_mirror 
# mount /dev/vg_data/lv_data01_mirror /mnt/data_mirror
# echo "foo" > /mnt/data_mirror/file.txt
# vgs
  VG      #PV #LV #SN Attr   VSize VFree
  vg_data   2   1   0 wz--n- 3.99g 3.02g
# pvs
  PV         VG      Fmt  Attr PSize PFree
  /dev/sdb   vg_data lvm2 a-   2.00g 1.51g
  /dev/sdc   vg_data lvm2 a-   2.00g 1.51g
# lvs
  LV               VG      Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  lv_data01_mirror vg_data mwi-ao 500.00m                        100.00

example 2 – (two disks, mirrorlog stored in RAM):
In case you have only two disk but you don’t want to keep the data in the RAM you need to create additional PVs on the same disks. In my opinion 5% of the cilinders is a good starting point

# fdisk -l /dev/sdb /dev/sdc | grep -e "cylinders" -e "dev"
Disk /dev/sdb: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
/dev/sdb1               1         247     1983996   8e  Linux LVM
/dev/sdb2             248         261      112455   8e  Linux LVM
Disk /dev/sdc: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
/dev/sdc1               1         247     1983996   8e  Linux LVM
/dev/sdc2             248         261      112455   8e  Linux LVM

# pvcreate /dev/sdb1 /dev/sdb2 /dev/sdc1 /dev/sdc2
# vgcreate vg_data /dev/sdb1 /dev/sdb2 /dev/sdc1 /dev/sdc2
  Volume group "vg_data" successfully created
# lvcreate -L 1988M -m1 --mirrorlog disk -n lv_data_mirror vg_data
  Logical volume "lv_data_mirror" created
# lvs
  LV             VG      Attr   LSize Origin Snap%  Move Log                 Copy%  Convert
  lv_data_mirror vg_data mwi-a- 1.94g                    lv_data_mirror_mlog 100.00   
# pvs
  PV         VG      Fmt  Attr PSize   PFree  
  /dev/sdb1  vg_data lvm2 a-     1.89g      0 
  /dev/sdb2  vg_data lvm2 a-   108.00m   4.00m
  /dev/sdc1  vg_data lvm2 a-     1.89g      0 
  /dev/sdc2  vg_data lvm2 a-   108.00m 104.00m

Snapshot Volume

# lvcreate –L100M –s –nlv_data01_snapshot /dev/vg_data/lv_data01
# mount /dev/vg_data/lv_data01_snapshot /data01_snapshot

example:

# lvcreate -L1G -n lv_data01 vg_data
# mkfs.ext4 /dev/vg_data/lv_data01 
# mkdir /mnt/data
# mount /dev/vg_data/lv_data01 /mnt/data/
# echo "foo" > /mnt/data/file.txt
# lvcreate -s -n lv_data01_snap -L 100M /dev/vg_data/lv_data01 
# mkdir /mnt/data_snap
# mount /dev/vg_data/lv_data01_snap /mnt/data_snap/
# df -h | grep data
/dev/mapper/vg_data-lv_data01       1022M   47M  924M   5% /mnt/data
/dev/mapper/vg_data-lv_data01_snap  1022M   47M  924M   5% /mnt/data_snap
# echo "bar" > /mnt/data/file.txt 
# cat /mnt/data/file.txt 
bar
# cat /mnt/data_snap/file.txt 
foo
# lvs
  LV             VG      Attr   LSize   Origin    Snap%  Move Log Copy%  Convert
  lv_data01      vg_data owi-ao   1.00g                                         
  lv_data01_snap vg_data swi-ao 100.00m lv_data01   0.08 
# lvresize -L 200M /dev/vg_data/lv_data01_snap 
  Extending logical volume lv_data01_snap to 200.00 MiB
  Logical volume lv_data01_snap successfully resized
# lvs
  LV             VG      Attr   LSize   Origin    Snap%  Move Log Copy%  Convert
  lv_data01      vg_data owi-ao   1.00g                                         
  lv_data01_snap vg_data swi-ao 200.00m lv_data01   0.04   
# umount /mnt/data_snap/
# lvremove /dev/vg_data/lv_data01_snap 
Do you really want to remove active logical volume lv_data01_snap? [y/n]: y
  Logical volume "lv_data01_snap" successfully removed

be carefull with the size of your snapshot. When it reaches 100% you can still write to the disk, but the snapshot is gone

# lvcreate -L 1G -n lv_data vg_data
# mkfs.ext4 /dev/vg_data/lv_data 
# mount /dev/vg_data/lv_data /mnt/data
# dd if=/dev/urandom of=/mnt/data/file20 bs=1M count=20
20971520 bytes (21 MB) copied, 2.39865 s, 8.7 MB/s
# dd if=/dev/urandom of=/mnt/data/file7 bs=1M count=7
7340032 bytes (7.3 MB) copied, 0.871878 s, 8.4 MB/s
# dd if=/dev/urandom of=/mnt/data/file12 bs=1M count=12
# lvcreate -s -L 10M -n lv_data_snap /dev/vg_data/lv_data 
# mount /dev/vg_data/lv_data_snap /mnt/data_snap/
# lvs
  LV           VG      Attr   LSize  Origin  Snap%  Move Log Copy%  Convert
  lv_data      vg_data owi-ao  1.00g                                       
  lv_data_snap vg_data swi-ao 12.00m lv_data   0.10                        
# dd if=/dev/urandom of=/mnt/data/file7 bs=1M count=7
7340032 bytes (7.3 MB) copied, 0.88662 s, 8.3 MB/s
# lvs
  LV           VG      Attr   LSize  Origin  Snap%  Move Log Copy%  Convert
  lv_data      vg_data owi-ao  1.00g                                       
  lv_data_snap vg_data swi-ao 12.00m lv_data  58.89                        
# dd if=/dev/urandom of=/mnt/data/file4 bs=1M count=4
4194304 bytes (4.2 MB) copied, 0.484525 s, 8.7 MB/s
# lvs
  LV           VG      Attr   LSize  Origin  Snap%  Move Log Copy%  Convert
  lv_data      vg_data owi-ao  1.00g                                       
  lv_data_snap vg_data swi-ao 12.00m lv_data  58.98                        
# dd if=/dev/urandom of=/mnt/data/file4 bs=1M count=23
24117248 bytes (24 MB) copied, 2.86702 s, 8.4 MB/s
# lvs
  /dev/vg_data/lv_data_snap: read failed after 0 of 4096 at 0: Input/output error
  LV           VG      Attr   LSize  Origin  Snap%  Move Log Copy%  Convert
  lv_data      vg_data owi-ao  1.00g                                       
  lv_data_snap vg_data Swi-Io 12.00m lv_data 100.00                        
root@bt:~# ls -l /mnt/data_snap/
ls: reading directory /mnt/data_snap/: Input/output error
total 0
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