Exercise: Fix three LVM problems

Fix three LVM problems

• Activate an inactive volume.
• Respond to Insufficient free space.
• Resolve a group that cannot be deactivated.

Start the exercise

On workstation, start the exercise. It builds the volume group vgdata on /dev/sdb2 of servera with the XFS volume lvstore (800 MiB, mounted on /srv/data) and the swap volume lvswap, both in /etc/fstab.

[student@workstation ~]$ lab start sa-lvm-troubleshooting

Later tasks assume that you are logged in to the server they name: ssh student@servera from workstation, then sudo -i for a root shell.

The starting point

On servera as root, make sure vgdata has the mounted volume lvstore on /srv/data (as left by the previous exercise).

[student@workstation ~]$ ssh student@servera
[student@servera ~]$ sudo -i
[root@servera ~]# lvs
  LV      VG     Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  lvstore vgdata -wi-ao---- 800.00m
  lvswap  vgdata -wi-ao---- 256.00m
[root@servera ~]# df -h /srv/data | tail -1
/dev/mapper/vgdata-lvstore  736M   38M  699M   6% /srv/data

Problem 1: the volume that does not exist

Unmount /srv/data and deactivate the volume lvstore (this simulates a volume that was not activated). Try mount -a. What does the error say, and what does lvs show in the Attr column? Fix it.

[root@servera ~]# umount /srv/data
[root@servera ~]# lvchange -an vgdata/lvstore
[root@servera ~]# lvs vgdata/lvstore
  LV      VG     Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  lvstore vgdata -wi------- 800.00m
[root@servera ~]# mount -a
mount: /srv/data: special device /dev/vgdata/lvstore does not exist.
[root@servera ~]# ls /dev/vgdata/
lvswap
[root@servera ~]# lvchange -ay vgdata/lvstore
[root@servera ~]# mount -a; df -h /srv/data | tail -1
/dev/mapper/vgdata-lvstore  736M   38M  699M   6% /srv/data

The a is missing from -wi-------: inactive, so no device file. After lvchange -ay it works.

Problem 2: not enough room

Try to extend lvstore by 2 GiB. Read the message, look at the group, and then extend it by what is possible, using +100%FREE.

[root@servera ~]# lvextend -r -L +2G /dev/vgdata/lvstore
  Insufficient free space: 512 extents needed, but only 119 available
[root@servera ~]# vgs
  VG     #PV #LV #SN Attr   VSize  VFree
  vgdata   1   2   0 wz--n- <1.50g 476.00m
[root@servera ~]# lvextend -r -l +100%FREE /dev/vgdata/lvstore | tail -1
  Logical volume vgdata/lvstore successfully resized.
[root@servera ~]# df -h /srv/data | tail -1
/dev/mapper/vgdata-lvstore  1.2G   42M  1.2G   4% /srv/data

The message says what the group has (119 extents of 4 MiB). To get more you would add a PV to the group; here we use what is there.

Problem 3: it will not deactivate

Try to deactivate the whole group vgdata while /srv/data is mounted and while swap is on. What does LVM tell you? Find out what is in use, free it, and deactivate the group. Then activate it again and restore the mounts.

[root@servera ~]# vgchange -an vgdata
  Can't deactivate volume group "vgdata" with 2 open logical volume(s)
[root@servera ~]# lvs -o lv_name,lv_attr
  LV      Attr
  lvstore -wi-ao----
  lvswap  -wi-ao----
[root@servera ~]# swapoff /dev/vgdata/lvswap; umount /srv/data
[root@servera ~]# vgchange -an vgdata
  0 logical volume(s) in volume group "vgdata" now active
[root@servera ~]# vgchange -ay vgdata
  2 logical volume(s) in volume group "vgdata" now active
[root@servera ~]# mount -a; swapon -a; df -h /srv/data | tail -1; swapon --show | tail -1
/dev/mapper/vgdata-lvstore  1.2G   42M  1.2G   4% /srv/data
/dev/dm-1 partition 256M   0B   -2

The o in -wi-ao---- means open: mounted or used as swap. The group deactivates only when nothing uses its volumes.

Save the layout, then clean up

Save the layout of the group with vgcfgbackup. Then remove everything you built in this chapter: unmount, remove the fstab lines (restore your backup), turn off swap, remove the volumes, the group and the physical volumes, and wipe the disk.

[root@servera ~]# vgcfgbackup vgdata
  Volume group "vgdata" successfully backed up.
  Logical volume "lvstore" successfully removed.
  Logical volume "lvswap" successfully removed.
  Volume group "vgdata" successfully removed
  Labels on physical volume "/dev/sdb2" successfully wiped.
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
sdb    8:16   0   5G  0 disk
[root@servera ~]# exit
[student@servera ~]$ exit

Order matters: volumes, then the group, then the PVs. rht-vmctl reset servers is the quick alternative.

Grade and finish

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