Exercise: Move data to a new disk

A volume holds your data on an old disk. Move it to a new disk while it stays mounted, retire the old disk, give the volume a better name, make everything permanent, add a swap volume, and prove it all with a reboot.

Move data to a new disk

Replace a PV with pvmove, vgreduce and pvremove.
Rename a volume and update fstab.
Add LVM swap and verify after a reboot.

Start the exercise

On workstation, start the exercise. It builds the volume group vgdata from the two partitions of /dev/sdb on servera, with the volumes lvapp and lvlog mounted on /srv/app and /srv/log.

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

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.

A fresh start

On servera as root, remove the volumes from the previous exercises (unmount them first), keep the volume group vgdata with both PVs, and create one volume lvdata of 800 MiB that lives only on /dev/sdb1. Put XFS on it, mount it on /srv/data, and write a file. Note its checksum. Check on which PV it lives.

[student@workstation ~]$ ssh student@servera
[student@servera ~]$ sudo -i
[root@servera ~]# umount /srv/app /srv/log 2> /dev/null
[root@servera ~]# lvremove -y vgdata/lvapp vgdata/lvlog
  Logical volume "lvapp" successfully removed.
  Logical volume "lvlog" successfully removed.
[root@servera ~]# lvcreate -y -n lvdata -L 800M vgdata /dev/sdb1
  Wiping xfs signature on /dev/vgdata/lvdata.
  Logical volume "lvdata" created.
[root@servera ~]# mkfs.xfs -f /dev/vgdata/lvdata > /dev/null
[root@servera ~]# mkdir -p /srv/data; mount /dev/vgdata/lvdata /srv/data
[root@servera ~]# seq 1 100000 > /srv/data/numbers.txt; sha256sum /srv/data/numbers.txt | cut -c1-16
b2bc7d3f8b652d2e
[root@servera ~]# lvs -o lv_name,devices vgdata; pvs -o pv_name,pv_size,pv_free
  LV     Devices
  lvdata /dev/sdb1(0)
  PV         PSize  PFree
  /dev/sdb1  <1.50g 732.00m
  /dev/sdb2  <1.50g  <1.50g

The final /dev/sdb1 on the lvcreate line tells LVM which PV to allocate from. If lvcreate asks about wiping an old signature, answer y. If sdb2 is not in the group yet, run pvcreate /dev/sdb2; vgextend vgdata /dev/sdb2 first.

Move the volume to sdb2

Move all the data off /dev/sdb1 onto /dev/sdb2, while /srv/data stays mounted. Check where the volume lives now and that the data is unchanged.

[root@servera ~]# pvmove /dev/sdb1 /dev/sdb2
  /dev/sdb1: Moved: 30.50%
  /dev/sdb1: Moved: 100.00%
[root@servera ~]# lvs -o lv_name,devices vgdata; pvs -o pv_name,pv_size,pv_free
  LV     Devices
  lvdata /dev/sdb2(0)
  PV         PSize  PFree
  /dev/sdb1  <1.50g  <1.50g
  /dev/sdb2  <1.50g 732.00m
[root@servera ~]# sha256sum /srv/data/numbers.txt | cut -c1-16
b2bc7d3f8b652d2e

The extents now live on sdb2, sdb1 is empty, and the checksum is the same.

Retire the old disk

Remove /dev/sdb1 from the volume group and wipe its LVM label.

[root@servera ~]# vgreduce vgdata /dev/sdb1
  Removed "/dev/sdb1" from volume group "vgdata"
[root@servera ~]# pvremove /dev/sdb1
  Labels on physical volume "/dev/sdb1" successfully wiped.
[root@servera ~]# vgs; pvs
  VG     #PV #LV #SN Attr   VSize  VFree
  vgdata   1   1   0 wz--n- <1.50g 732.00m
  PV         VG     Fmt  Attr PSize  PFree
  /dev/sdb2  vgdata lvm2 a--  <1.50g 732.00m

Rename, and make it permanent

Rename lvdata to lvstore. Add an fstab line for it (by LV path), verify, and mount it from fstab.

[root@servera ~]# umount /srv/data
[root@servera ~]# lvrename vgdata lvdata lvstore
  Renamed "lvdata" to "lvstore" in volume group "vgdata"
[root@servera ~]# cp /etc/fstab /root/fstab.bak
[root@servera ~]# echo "/dev/vgdata/lvstore  /srv/data  xfs  defaults  0 0" >> /etc/fstab
[root@servera ~]# systemctl daemon-reload; findmnt --verify | tail -1
0 parse errors, 0 errors, 1 warning
[root@servera ~]# mount -a; df -h /srv/data | tail -1
/dev/mapper/vgdata-lvstore  736M   38M  699M   6% /srv/data

Swap on a volume

Create a 256 MiB volume lvswap, prepare it as swap, add it to fstab, and enable all swap with swapon -a.

[root@servera ~]# lvcreate -n lvswap -L 256M vgdata
  Logical volume "lvswap" created.
[root@servera ~]# mkswap /dev/vgdata/lvswap
Setting up swapspace version 1, size = 256 MiB (268431360 bytes)
[root@servera ~]# echo "/dev/vgdata/lvswap  none  swap  defaults  0 0" >> /etc/fstab
[root@servera ~]# systemctl daemon-reload; swapon -a; swapon --show
NAME      TYPE      SIZE USED PRIO
/dev/dm-1 partition 256M   0B   -2

Reboot and check

Reboot, log in again, and check the mount, the swap, the group and the data.

[root@servera ~]# systemctl reboot
[student@workstation ~]$ ssh student@servera
[student@servera ~]$ df -h /srv/data | tail -1; swapon --show | tail -1; sudo vgs; sha256sum /srv/data/numbers.txt | cut -c1-16
/dev/mapper/vgdata-lvstore  736M   38M  699M   6% /srv/data
/dev/dm-1 partition 256M   0B   -2
  VG     #PV #LV #SN Attr   VSize  VFree
  vgdata   1   2   0 wz--n- <1.50g 476.00m
b2bc7d3f8b652d2e
[student@servera ~]$ exit

Volumes activate by themselves at boot, and the data is exactly what you wrote. Keep this layout for the troubleshooting exercise.

Grade and finish

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