Linux Training : l. LVM

LVM

• Logical Volume Management aggregates drives

  LVM is a way to manage storage space so the filesystem can grow as needed. In general, once the filesystem is established and all drives mounted, making changes is very difficult if a partition runs out of room. If /var fills up, the system halts (
  Unknown macro: {tm}

  VeryBadThing

  ). With LVM, the filesystem can be expanded without having to copy all the data to a larger drive. For the most part here, LVM is used during the initial installation and rarely is it used afterwards.

  • Physical groups

    Physical groups are the actual drive partitions themselves.

    /usr/sbin/pvscan
      PV /dev/sda2   VG VolGroup70   lvm2 [148.94 GB / 0    free]
      Total: 1 [148.94 GB] / in use: 1 [148.94 GB] / in no VG: 0 [0   ]
    

    This shows a single physical volume group that uses sda2 partition and it all allocated to VolGroup70

  • Volume groups

    These are the structures on top of the physical groups. They are used to form the bases for the filesystem mount point.

     /usr/sbin/vgscan
      Reading all physical volumes.  This may take a while...
      Found volume group "VolGroup70" using metadata type lvm2
    

  • Logical volumes

    These are partitions created from the Volume groups.

    /usr/sbin/lvscan
      ACTIVE            '/dev/VolGroup70/LvRoot' [143.94 GB] inherit
      ACTIVE            '/dev/VolGroup70/LvLogs' [4.00 GB] inherit
      ACTIVE            '/dev/VolGroup70/LvSwap' [1.00 GB] inherit
    

    These logical partition match what mount says is mounted (swap is not "mounted" it is simply used)

     mount
    /dev/mapper/VolGroup70-LvRoot on / type ext3 (rw)
    proc on /proc type proc (rw)
    sysfs on /sys type sysfs (rw)
    devpts on /dev/pts type devpts (rw,gid=5,mode=620)
    /dev/mapper/VolGroup70-LvLogs on /var/log type ext3 (rw)
    /dev/sda1 on /boot type ext3 (rw)
    tmpfs on /dev/shm type tmpfs (rw)
    none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)