Exercise: LVM review

LVM review

• Build PV, VG and LVs with a chosen extent size.
• Add a PV when the group is full and extend a mounted volume.
• Make mounts and swap permanent.

Before you start: reset the servers and complete this chapter's lessons. You work on serverb as root (sudo -i), on the spare disk /dev/sdb; lab start and lab grade run on workstation.

On serverb:

1. Create two LVM partitions of 1.5 GiB on /dev/sdb.
2. Create the volume group vgapp on the first one with 8 MiB extents.
3. Create lvweb (1 GiB, XFS, /srv/web), lvdb (400 MiB, ext4, /srv/db) and lvswap (256 MiB, swap). When the group is full, add the second partition.
4. Write seq 1 100000 into /srv/web/numbers.txt, then extend lvweb to at least 2000 MiB while it is mounted.
5. Make everything permanent in /etc/fstab and test it.
6. On workstation, fill in answers.txt.

Start the exercise

[student@workstation ~]$ lab start sa-lvm-review
[student@workstation ~]$ ssh student@serverb
[student@serverb ~]$ sudo -i
[root@serverb ~]#

Partitions, group and the first volumes

[root@serverb ~]# parted -s /dev/sdb mklabel gpt mkpart pv1 1MiB 1537MiB mkpart pv2 1537MiB 3073MiB set 1 lvm on set 2 lvm on
[root@serverb ~]# udevadm settle
[root@serverb ~]# pvcreate /dev/sdb1
[root@serverb ~]# vgcreate -s 8M vgapp /dev/sdb1
[root@serverb ~]# lvcreate -n lvweb -L 1G vgapp
[root@serverb ~]# lvcreate -n lvdb -L 400M vgapp
[root@serverb ~]# lvcreate -n lvswap -L 256M vgapp
  Volume group "vgapp" has insufficient free space (13 extents): 32 required.
[root@serverb ~]# pvcreate /dev/sdb2; vgextend vgapp /dev/sdb2
[root@serverb ~]# lvcreate -n lvswap -L 256M vgapp
  Logical volume "lvswap" created.
[root@serverb ~]# vgs -o vg_name,pv_count,vg_extent_size,vg_size,vg_free vgapp
  VG    #PV Ext    VSize VFree
  vgapp   2 8.00m 2.98g 1.34g

With 8 MiB extents, 256 MiB needs 32 extents and the group had only 13 left, hence the message.

File systems, data and the online extension

[root@serverb ~]# mkfs.xfs /dev/vgapp/lvweb > /dev/null
[root@serverb ~]# mkfs.ext4 /dev/vgapp/lvdb > /dev/null 2>&1
[root@serverb ~]# mkswap /dev/vgapp/lvswap
[root@serverb ~]# mkdir -p /srv/web /srv/db
[root@serverb ~]# mount /dev/vgapp/lvweb /srv/web; mount /dev/vgapp/lvdb /srv/db
[root@serverb ~]# seq 1 100000 > /srv/web/numbers.txt
[root@serverb ~]# lvextend -r -L 2G /dev/vgapp/lvweb
  Extended file system xfs on vgapp/lvweb.
  Logical volume vgapp/lvweb successfully resized.
[root@serverb ~]# df -h /srv/web | tail -1; tail -1 /srv/web/numbers.txt
/dev/mapper/vgapp-lvweb  2.0G   51M  1.9G   3% /srv/web
100000

Permanent, and test

[root@serverb ~]# cp /etc/fstab /root/fstab.bak
[root@serverb ~]# cat >> /etc/fstab <<'EOT'
/dev/vgapp/lvweb   /srv/web  xfs   defaults  0 0
/dev/vgapp/lvdb    /srv/db   ext4  defaults  0 0
/dev/vgapp/lvswap  none      swap  defaults  0 0
EOT
[root@serverb ~]# systemctl daemon-reload; findmnt --verify | tail -1
0 parse errors, 0 errors, 1 warning
[root@serverb ~]# mount -a && swapon -a; df -hT /srv/web /srv/db | tail -2; swapon --show

A reboot (systemctl reboot) is the final proof. Afterwards check vgs, lvs and the mounts again.

Grade

On workstation, fill in answers.txt and grade:

Check your work with lab grade sa-lvm-review, then put the exercise away with lab finish sa-lvm-review.