☩ Walking in Light with Christ – Faith, Computing, Diary

Many Linux servers these days are using LVM (Logical Volume Manager) in order to allow disk drives and partitions to be easily managed (shrinked / resized).  It is interesting fact LVM is successor of HP-UX's volume manager. LVM can be considered as a thin software layer on top of the hard disks and partitions, which creates an abstraction of continuity and ease-of-use for managing hard drive replacement, re-partitioning, and backup.

 

LVM is commonly used for the following purposes:

• Managing large hard disk farms by allowing disks to be added and replaced without downtimes and services disruption (useful whenever hot-swapping is needed)
• On small systems (like a desktop at home), instead of having to estimate at installation time how big a partition might need to be in the future.
  – LVM lets file systems to be easily resized later as needed.
• Performing consistent backups by taking snapshots of the logical volumes.
• Creating single logical volumens of multiple physical volumes or entire hard disks (somewhat similar to RAID-0), ability to do dynamic volume resizing (in LVM partitions are volumes).

So if you're sysadmin it is quite likely that some LVM volume starts being filled up (because of bad initial planning), so the customer asks you to resize a LVM (volume), here is how to do it:

1. Check whether LVM configured on server has free disk space that can be relocated
First lets list all LVM configured volumes on server:

# vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "web_log" using metadata type lvm2
  Found volume group "web_all" using metadata type lvm2
  Found volume group "rootvg" using metadata type lvm2

vgscan – scan all disks for volume groups and rebuild caches
Then lets display the volume group information.

This is done with vgdisplay cmd
 # vgdisplay
  --- Volume group ---
  VG Name               rootvg
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  13
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                11
  Open LV               11
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               136.56 GB
  PE Size               8.00 MB
  Total PE              17480
  Alloc PE / Size       7329 / 57.26 GB
  Free  PE / Size       10151 / 79.30 GB
  VG UUID               27z2w0-Ku0H-y6M0-QFCR-3Rp6-c1HX-OTinzn

[root@lupus ~]# vgs
  VG         #PV #LV #SN Attr   VSize   VFree
  VolGroup00   1   3   0 wz–n- 695.44G    0
[root@lupus ~]# pvs
  PV         VG         Fmt  Attr PSize   PFree
  /dev/sda3  VolGroup00 lvm2 a–  695.44G    0

Important line from above command output is (Free  PE / Size       10151 / 79.30 GB). Indicating that server's LVM had 79.30 GB Free which can be used to extend any of the server LVM existing volumes.

Here are one of servers managed by me existing volumes:

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/rootvg-root
                      5.0G  301M  4.4G   7% /
udev                   18G  144K   18G   1% /dev
tmpfs                  42G     0   42G   0% /dev/shm
/dev/cciss/c0d0p1     122M   28M   88M  24% /boot
/dev/mapper/rootvg-home
                      512M  268M  219M  56% /home
/dev/mapper/rootvg-opt
                      2.5G  484M  1.9G  21% /opt
/dev/mapper/rootvg-Tivoli
                      3.0G  895M  2.0G  32% /opt/Tivoli
/dev/mapper/rootvg-uc4
                      3.0G  289M  2.6G  11% /opt/uc4
/dev/mapper/rootvg-sysadm
                      3.0G   69M  2.8G   3% /sysadm
/dev/mapper/rootvg-tmp
                      1.3G   35M  1.2G   3% /tmp
/dev/mapper/rootvg-usr
                      4.0G  1.2G  2.6G  32% /usr
/dev/mapper/rootvg-var
                      5.0G  500M  4.2G  11% /var
/dev/mapper/rootvg-webservices
                      9.9G  4.0G  5.9G  41% /webservices
 

For instance lets say the task is to extend LVM (volume) partition:

/dev/mapper/rootvg-webservices
                      9.9G  4.0G  5.9G  41% /webservices

Lets say we want to extend /dev/mapper/rootvg/rootvg-webserices with 20 Gygabytes:
 

# lvextend -L20G /dev/mapper/rootvg-webservices

Then we we would like to add some extra 10GB:

# lvextend -L10G /dev/mapper/rootvg-webservices

In order to add all available LVM free space to a volume use:
 

# lvextend -l +100%FREE /dev/mapper/rootvg-webservices

Whether you had to do it on Linux with kernel 2.4.x and ext2 / ext3 FS:
 

# umount /dev/mapper/rootvg-webservices
# resize2fs /dev/mapper/rootvg-webservices
# mount /dev/mapper/rootvg /webservices

To resize ext4 filesystem with LVM above umount / resize2fs and mount commands can be safely skipped.

On other file systems to raise the size of the filesystem there are different tools to use also on some umount and mount is not necessary example for dynamicly resizable filesystem is reiserfs (though I don't recommend this FS to anyone as the creator of ReiserFS killed his family – moreover my personal experience with ReiserFS in past was quite bitter – I lost personal data because of ReiserFS break ups).

Here is how to dynamicly resize FS after lvextend on Reiserfs filesystem:
 

# resize_reiserfs -f /dev/myvg/homevol

XFS also supports resize of filesystem with no need to re-mount on server with XFS LVM resize after lvextend run:
 

# xfs_growfs /webservices