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1. LVM
VIMAL THAMIZHARASAN
SENIOR LINUX TRAINER
MAZENET SOLUTION-CHENNAI,T-NAGAR.

2. Agenda
• Some basic background about Files and
Filesystems under Linux
• What is LVM and why should I use it
• How to create a simple LVM environment

3. What is Logical Volume Management?
• Software that allows the user to edit the
storage configuration without
• manipulating the actual hardware and vice
versa.

4. When to and not use LVMs
• USE WHEN:
-Lots of DISKs and you need to simplify
-Need flexiblity of file system expansion
-When you want to learn an advanced storage
management topic
• DON'T USE:
-SINGLE Partition Environments
-If Command line (CLI) is scary to you
-Without access to a System Administrator :

5. How Does LVM Work?
The LVM hides information
about where information is
stored, on which hardware,
and where exactly on that
hardware from the entire
Operating System allowing
it to manipulate the
configuration of the storage
capacities.

6. Layers to make it easier
• Layers in a typical system (before LVM)
Files/Dirs
Filesystems
Partitions
Disks

7. What is a Disk?
• The harddisk is the only Hardware piece we're
going to talk about here
• It has various techie things in it:
- Cylinders, Heads, Sectors, mbr, partitions
- It's own cpu, cache, firmware etc.
• but for this discussion a hard disk on a modern
system can be seen as one continuous row of
logical blocks.
• Typical disk names in Linux are hda, sda,vda.

8. Partitions
• To store data on a disk this continuous row of
logical blocks needs to be cut in sections called
Partitions.
• The original IBM PC from 1981 only had 4 primary
partitions.
• This was later improved by adding extended partitions
• Normally managed by fdisk or some graphical
partition/volume manager.
• One partition must be a continuous chunk of blocks .

9. Filesystems
• Filesystems are a fancy way to hold together a
group of files and directories.
• Without LVM one filesystem=one partition.
• Common File Systems:
-In the Windows World:
FAT (dos) FAT12/16/32
NTFS
-In Linux
Ext2/3, Reiserfs,jfs,xfs
And many many more

10. Files on a linux (and unix) system
• At last we are at the top, the user level
• Within User Level we have
–Files
–Directories
–Filesystems
Files Hold Data
• Directories hold files and directories
• Filesystems holds directories and files
• Mount points hold Filesystems

11. Time for volumes
Volumes

12. • By adding another layer between partitions
and filesystems we break the
OneFS=OnePartition relation
• This have many advantages
• 2 special reasons:
–Can carve out non continues filesystems
–Can add disks partitions together so they
look like one big disk

13. Commands used in LVM
Directory and Files
Directories and Files
## Directories
/etc/lvm - default lvm directory location
/etc/lvm/backup - where the automatic backups go
/etc/lvm/cache - persistent filter cache
/etc/lvm/archive - where automatic archives go after a volume group change
/var/lock/lvm - lock files to prevent metadata corruption
# Files
/etc/lvm/lvm.conf - main lvm configuration file
$HOME/.lvm - lvm history
Physical Volumes
display
pvdisplay -v
pvs -v
pvs -a

14. Commands used in LVM
adding
pvcreate /dev/sdb1
## Create physical volume with specific UUID, used to recover volume groups (see
miscellaneous section)
pvcreate --uuid <UUID> /dev/sdb1
removing pvremove /dev/sdb1
moving
pvmove -v /dev/sdb2 /dev/sdb3
Note: moves any used extents from this volume to another volume, in readiness to remove that
volume. However you cannot use this on mirrored volumes, you must convert back to non-
mirror using "lvconvert -m 0"
Volume Groups
creating
vgcreate VolData00 /dev/sdb1 /dev/sdb2 /dev/sdb3
vgcreate VolData00 /dev/sdb[123]
vgcreate VolData00 -s 32 /dev/sdb1
Common Attributes that you may want to use:
-l maximum logical volumes
-p maximum physical volumes
-s physical extent size (default is 4MB)
-A autobackup

15. Commands used in LVM
extending vgextend VolData00 /dev/sdb3
reducing
vgreduce VolData00 /dev/sdb3
vgreduce --removemissing --force VolData00
removing
vgremove VolData00
Common Attributes that you may want to use:
-f force the removal of any logical volumes
merging
# the old volumes group will be merged into the new volume group
vgmerge New_Vol_Group Old_Vol_Group
Note: you must unmount any fielsystems and deactivate the vg that is being
merged "vgchange -a n <vg>", then you can activiate it again afterwards
"vgchange -a y <vg>", then perform a vgscan, dont forget to backup the
configuration
spliting
vgsplit Old_Vol_Group New_Vol_Group [physical volumes] [-n logical
volume name]

16. Commands used in LVM
Logical Volumes
display
lvdisplay -v
lvdisplay --maps display mirror volumes
lvs -v
lvs -a -o +devices
## lvs commands for mirror volumes
lvs -a -o +devices
lvs -a -o +seg_pe_ranges --segments
## Stripe size
lvs -v --segments
lvs -a -o +stripes,stripesize
scanning
lvscan -v
lvmdiskscan
creating
## plain old volume
lvcreate -L 10M VolData00
## plain old volume but with a specific name web01
lvcreate -L 10M -n web01 VolData00
## plain old volume but on a specific disk
lvcreate -L 10M VolData00 /dev/sdb1
## a striped volume called lvol1 (note the captial i for the stripe size), can use -l
(extents) instead of -L
lvcreate -i 3 -L 24M -n lvol1 vg01

17. extending
lvextend -L 20M /dev/VolData00/vol01
Note: you can extend a ext2/ext3 filesystem using the "resize2fs" or "fsadm"
command
fsadm resize /dev/VolData01/data01
resize2fs -p /dev/mapper/VolData01-data01 [size]
The -p option displays bars of progress while extendingthe filesystem
reducing/resizing
lvreduce -L 5M /dev/VolData00/vol01
lvresize -L 5M /dev/VolData00/vol01
Note: rounding will occur when extending and reducing volumes to the next extent
(4MB by default), you can use resize2fs or fsadm to shrink the filesystem
fsadm resize /dev/VolData01/data01 [size]
resize2fs -p /dev/mapper/VolData01-data01 [size]
removing lvremove /dev/VolData00/vol01

18. THANK YOU ALL