LogicalVolumeManagement/SettingUpVolumes

This section is based on the "recipe" from the LVM HOWTO at http://www.tldp.org/HOWTO/LVM-HOWTO/recipethreescsi.html. It covers setting up a LVM system spanning two physical hard disks.

1. The device node /dev/mapper/control is not created automatically under Debian Woody, although it may be present under other environments. To create it yourself you must first create the directory /dev/mapper using the mkdir command:

mkdir /dev/mapper

1. Create the device node using the mknod command:

mknod /dev/mapper/control c 10 63

1. Run pvcreate on each of the hard disks (physical volumes) you want to use with LVM. This will destroy all data on the disk! For example:

    holly:/# pvcreate /dev/sda
{{{
    No physical volume label read from /dev/sda
    Physical volume "/dev/sda" successfully created
    holly:/# pvcreate /dev/sdb
    No physical volume label read from /dev/sdb
    Physical volume "/dev/sdb" successfully created

1. Run vgcreate to add the physical volumes you prepared to a volume group. For example:

    holly:/# vgcreate vol_grp1 /dev/sda /dev/sdb
    Volume group "vol_grp1" successfully created

1. You can now use the vgdisplay command to display information about your volume group. The information shown will of course differ on your system, depending on its specifcation:

holly:/# vgdisplay
  --- Volume group ---
  VG Name               vol_grp1
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                256
  Cur LV                0
  Open LV               0
  Max PV                256
  Cur PV                1
  Act PV                1
  VG Size               68.50 GB
  PE Size               4.00 MB
  Total PE              17537
  Alloc PE / Size       0 / 0   
  Free  PE / Size       17537 / 68.50 GB
  VG UUID               [[TwfyDg]]-[[QDmI]]-GEzl-fYBx-b01P-8Y9a-[[Mv4lYt]]

1. Use the lvcreate command to create a logical volume on top of the volume group. You have to specify a size for the logical volume using the -L option and the name for the logical volume with the -n option. In this example, I will make the logical volume occupy all the space available in the volume group. I will use the 68.50 GB figure from the vgdisplay command above:

lvcreate -L68.50G  -nlog_vol1 vol_grp1
  Logical volume "log_vol1" created

1. You can view information about your newly created logical volume using the lvdisplay command:

holly:/# lvdisplay
  --- Logical volume ---
  LV Name                /dev/vol_grp1/log_vol1
  VG Name                vol_grp1
  LV UUID                9dErU7-YDsg-YDbh-SEWR-yVo6-Wc!0-[[RBqXke]]
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                68.50 GB
  Current LE             17536
  Segments               1
  Allocation             next free (default)
  Read ahead sectors     0
  Block device           254:0

1. Now it's time to create a filesystem on the logical volume (analogous to formatting a hard disk partition.) This example creates an ext3 filesystem using the standard Linux commands:

holly:/# mke2fs /dev/vol_grp1/log_vol1
mke2fs 1.27 (8-Mar-2002)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)

Fragment size=4096 (log=2) 8978432 inodes, 17956864 blocks 897843 blocks (5.00%) reserved for the super user First data block=0 548 block groups 32768 blocks per group, 32768 fragments per group 16384 inodes per group Superblock backups stored on blocks:

        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624, 11239424

Writing inode tables: done Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 21 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override. holly:/# tune2fs -j /dev/vol_grp1/log_vol1 tune2fs 1.27 (8-Mar-2002) Creating journal inode: done This filesystem will be automatically checked every 21 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override. }}}

1. Now it remains to mount and test the new filesystem. This is done by using the standard mount command:

holly:/# mount /dev/vol_grp1/log_vol1 /mnt

1. Your new filesystem should now be mounted and ready to have data written to it. You can, of course, mount the filesystem in some other location such as /home and you can add a line to /etc/fstab to have it mounted automatically on system boot. For example, this line will mount the logical volume at /home automatically on system boot:

/dev/vol_grp1/log_vol1 /home    ext3    defaults                0       2