LVM Management

What is LVM

If a system is partitioned with the ext3 file system, the hard drive is divided into partitions of defined sizes. If a partition becomes full, it is not easy to expand the size of the partition. Even if the partition is moved to another hard drive, the original hard drive space has to be reallocated as a different partition or not used

LVM Resize Actions

When shrinking, you should perform actions in this order

i) Resize the file system

ii) Resize the logical volume

When growing, you should perform actions in this order

i) Resize the logical volume

ii) Resize the file system

With the Help of LVM commands

a) To create LVM

To create a LVM volume we need to create Physical volume and volume group first. 

# pvcreate /dev/sda1 /dev/sdb1 /dev/sdc1

# vgcreate new_vol_group /dev/sda1 /dev/sdb1 /dev/sdc1

# lvcreate -L 2 G -n new_logical_volume new_vol_group

# mkfs.gfs2 -p lock_nolock -j 1 /dev/new_vol_group/new_logical_volume

# mount /dev/new_vol_group/new_logical_volume /mnt

b) To increase LVM size

# lvextend -L +100%FREE /dev/ubuntu-box-1-vg/root

# lvextend -L 100%FREE /dev/VolGroup00/lv_root

Note: When resizing a logical volume with the following command, it is try to resize it to the number of free extents, rather than the current size plus the number of free extents

Use the + symbol in front of X%FREE to indicate the space should be added to the current size.

# lvextend -L +100%FREE /dev/volgroup/logvo

lvresize -rL 30G /dev/vg_proxy/lv_root

lvresize -rL +5G /dev/vg_proxy/lv_root

which mitigates the need to resize in a particular order and drastically reduces the potential for erro

c.1) How to reduce LVM size

To Reduce, the LVM we need to first unmount the volume
# umount

Then execute resize2fs command with the final size what we want eg: from 100GB to 80GB then

# resize2fs filesystem <final size>

# After executing resize2fs command reduce the volume size, using lVM then mount it.
lvreduce -L 80G

Note :  Partition types : lvm - 8e, swap - 82, linux - 83

lvresize --resizefs --size SIZE /dev/vg/vg_data

d) How to remove a physical volume from a LVM

If there are enough free extents on the other physical volumes in the volume group, you can execute the pvmove command on the device you want to remove with no other options and the extents will be distributed to the other devices.

To check the usage of physical volumes
# pvs -o+pv_used

If free space is there, then use pvmove command to move the data from the volume
# pvmove /dev/sdb1

Then remove the physical volume from the volume group by using vgreduce command.
# vgreduce myvg /dev/sdb1

How to move data to a new HDD

There may be a case where 

First create physical volume with the new disk 
# pvcreate /dev/sdd1

Extend the Volume group with the new disk

# vgextend myvg /dev/sdd1

Now, move the data from OLD disk to NEW disk using pvmove command
# pvmove <Old Disk> <New Disk>

# pvmove /dev/sdb1 /dev/sdd1

Once if the data is copied, remove the old disk from volume group by using vgreduce command
# vgreduce myvg /dev/sdb1

How to LVM mirroring

Link http://www.tecmint.com/lvm-storage-migration/ Steps works fine except for one option.

We need some space for mirror logs while mirroring so --mirrorlog core/--alloc anywhere option can be used.

--mirrorlog core  à The log can be kept in memory so that no extra physical volume is needed to mirror the device

--alloc anywhere à the size of the mirror has to be smaller than the size of total physical volumes because the mirror log requires that free space.

@XXXXX~]# lvconvert -m 1 --mirrorlog core /dev/vgtest/lvtest /dev/sde

  vgtest/lvtest: Converted: 0.6%

  vgtest/lvtest: Converted: 8.7%

  vgtest/lvtest: Converted: 26.4%

  vgtest/lvtest: Converted: 63.9%

  vgtest/lvtest: Converted: 100.0%

@XXXXX~]# lvconvert -m 0 /dev/vgtest/lvtest /dev/sdd

  Logical volume lvtest converted.

@XXXXX~]# lvs -o +devices

  LV       VG       Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices

  lvvar    vgsystem -wi-ao----   2.48g                                                     /dev/sda2(384)

  lvvar    vgsystem -wi-ao----   2.48g                                                     /dev/sda2(896)

  lvtest   vgtest   -wi-ao----   5.00g                                                     /dev/sde(0)

@XXXXXtest]# df -h .

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/vgtest-lvtest

                      4.8G  1.8G  2.8G  39% /test

Mirroring took hardly 3 mins for 2G of data.

2) Using dmsetup command

dmsetup is low level LVM command. Using dmsetup we can manage LVM's

UUID duplicate error

Figured it out. I was using kpartx for backups a few months ago and forgot to close the devices with kpartx -d. I discover using partprobe that the lvm volumes wich belong to virtual machines are "exported" to to the server,and fill /dev/mapper with duplicates lvms,so i used kpartx -d to all devices in /dev/mapper and situation return ok. lvs,pvs,vgs didn't give any error mess

uuidgen

tune2fs -U <output of uuidgen> /dev/sdb1

Or if you're confident uuidgen is going to work:

tune2fs -U `uuidgen` /dev/sdb1