Managing Disk Space with LVM -02

Basically LVM looks like this:



You have one or more physical volumes (/dev/sdb1 - /dev/sde1 in our example), and on these physical volumes you create one or more volume groups (e.g. fileserver), and in each volume group you can create one or more logical volumes. If you use multiple physical volumes, each logical volume can be bigger than one of the underlying physical volumes (but of course the sum of the logical volumes cannot exceed the total space offered by the physical volumes).
It is a good practice to not allocate the full space to logical volumes, but leave some space unused. That way you can enlarge one or more logical volumes later on if you feel the need for it.
In this example we will create a volume group called fileserver, and we will also create the logical volumes /dev/fileserver/share, /dev/fileserver/backup, and /dev/fileserver/media (which will use only half of the space offered by our physical volumes for now - that way we can switch to RAID1 later on (also described in this tutorial)).


Now we prepare our new partitions for LVM:

kilo:~# pvcreate /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
  Physical volume "/dev/sdb1" successfully created
  Physical volume "/dev/sdc1" successfully created
  Physical volume "/dev/sdd1" successfully created
  Physical volume "/dev/sde1" successfully created

Let's revert this last action for training purposes:

kilo:~# pvremove /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
  Labels on physical volume "/dev/sdb1" successfully wiped
  Labels on physical volume "/dev/sdc1" successfully wiped
  Labels on physical volume "/dev/sdd1" successfully wiped
  Labels on physical volume "/dev/sde1" successfully wiped

kilo:~# pvdisplay
  --- NEW Physical volume ---
  PV Name               /dev/sdb1
  . . . 
Now let's create our volume group fileserver and add /dev/sdb1 - /dev/sde1 to it:

kilo:~# vgcreate fileserver /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
  Volume group "fileserver" successfully created

Let's learn about our volume groups:

vgdisplay

server1:~# vgdisplay
  --- Volume group ---
  VG Name               fileserver

Another command to learn about our volume groups:
kilo:~# vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "fileserver" using metadata type lvm2

Next we create our logical volumes share (40GB), backup (5GB), and media (1GB) in the volume group fileserver. Together they use a little less than 50% of the available space (that way we can make use of RAID1 later on):kilo:~# lvcreate --name share  --size 40G fileserver
  Logical volume "share" created
kilo:~# lvcreate --name backup --size  5G fileserver
  Logical volume "backup" created
kilo:~# lvcreate --name media  --size  1G fileserver
  Logical volume "media" created 
kilo:~# lvdisplay
  --- Logical volume ---
  LV Name                /dev/fileserver/share
  VG Name                fileserver
  LV UUID                280Mup-H9aa-sn0S-AXH3-04cP-V6p9-lfoGgJ
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                40.00 GB
  Current LE             10240
  Segments               2
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:0

  --- Logical volume ---
  LV Name                /dev/fileserver/backup
  VG Name                fileserver
  LV UUID                zZeuKg-Dazh-aZMC-Aa99-KUSt-J6ET-KRe0cD
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                5.00 GB
  Current LE             1280
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:1

  --- Logical volume ---
  LV Name                /dev/fileserver/media
  VG Name                fileserver
  LV UUID                usfvrv-BC92-3pFH-2NW0-2N3e-6ERQ-4Sj7YS
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                1.00 GB
  Current LE             256
  Segments               1
  Allocation             inherit
  Read ahead sectors     0
  Block device           253:2
kilo:~# lvscan
  ACTIVE            '/dev/fileserver/share' [40.00 GB] inherit
  ACTIVE            '/dev/fileserver/backup' [5.00 GB] inherit
  ACTIVE            '/dev/fileserver/media' [1.00 GB] inherit


Until now we have three logical volumes, but we don't have any filesystems in them, and without a filesystem we can't save anything in them. Therefore we create an ext3 filesystem in share, an xfs filesystem in backup, and a reiserfs filesystem in media:
 kilo:~# mkfs.ext3 /dev/fileserver/share

mke2fs 1.40-WIP (14-Nov-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
5242880 inodes, 10485760 blocks
524288 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
320 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

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 23 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.

kilo:~# mkdir /var/media /var/backup /var/share
kilo:~#   mount /dev/fileserver/share /var/sharekilo:~#  mount /dev/fileserver/backup /var/backupkilo:~#  mount /dev/fileserver/media /var/media
kilo:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              19G  665M   17G   4% /
tmpfs                  78M     0   78M   0% /lib/init/rw
udev                   10M   88K   10M   1% /dev
tmpfs                  78M     0   78M   0% /dev/shm
/dev/sda1             137M   17M  114M  13% /boot
/dev/mapper/fileserver-share
                       40G  177M   38G   1% /var/share
/dev/mapper/fileserver-backup
                      5.0G  144K  5.0G   1% /var/backup
/dev/mapper/fileserver-media
                      1.0G   33M  992M   4% /var/media

kilo:~# vi /etc/fstab

/dev/fileserver/share   /var/share     ext3       rw,noatime    0 0
/dev/fileserver/backup    /var/backup      xfs        rw,noatime    0 0
/dev/fileserver/media    /var/media      reiserfs   rw,noatime    0 0