Logical Volume Management

Logical Volume Management (LVM)

1 Initial partitioning by clean CentOS installation

Automatic partitioning of 120-GiB SSD by clean CentOS-8.1 installation as follows

• /dev/sda1       1 GiB   ext4         /boot
• /dev/sda2   118 GiB   lvm2_pv   cl     (cl: volume group name)
  • /dev/mapper/cl-swap     8 GiB     swap
  • /dev/mapper/cl-root     50 GiB   XFS   /
  • /dev/mapper/cl-home   60 GiB   XFS   /home

Basic commands to display LVM information

• vgdisplay will display volume group information

• pvdisplay will display physical volume information

• lvdisplay will display logical volume information

2 Custom partitioning

2.1 Objective

• /boot   (unchanged)
• swap   (unchanged)
• /   (unchanged)
• /home   (XFS reduced to 20 GiB)
• /data1   (new 20 GiB ext4)
• /data2   (new 20 GiB ext4)

XFS doesn't support partition shrinking (scale-down), so the logical volume hosting /home needs first to be deleted and re-created with the scaled-down size.

2.2 How to

• Backup /home
  • xfsdump -l 0 -f /var/tmp/home.backup /home
    • label? dump-1   (name doesn't matter)
    • label? dump-2   (name doesn't matter)

• Reset /home
  • umount /home
  • lvremove /dev/mapper/cl-home
  • lvcreate -L 20G --name home cl
  • mkfs.xfs /dev/mapper/cl-home
  • mount /home
  • xfsrestore -f /var/tmp/home.backup /home
  • rm /var/tmp/home.backup

• Create /data1 and /data2 filesystems
  • lvcreate --name data1 -L 20G cl
  • lvcreate --name data2 -l 100%FREE cl
  • mkfs.ext4 /dev/mapper/cl-data1
  • mkfs.ext4 /dev/mapper/cl-data2
  • mkdir /data1 /data2
  • edit /etc/fstab
    • /dev/mapper/cl-data1 /data1 ext4 defaults 0 0
    • /dev/mapper/cl-data2 /data2 ext4 defaults 0 0
  • mount -a

• Create /data{1|2}/tmp directory accessible to everyone
  • mkdir /data1/tmp /data2/tmp
  • chmod a+trwx /data1/tmp /data2/tmp   (only user - or root - can remove files)

3 See also

• Linux Unified Key Setup