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Updating the OS using LVM as a snapshots.

Most info from
  https://www.suse.com/c/rollback-sles-online-updates-lvm-snapshots/
However the images of the process is missing

Setup..
  /boot       normal partition
  / & /home   LVM

Prepare
  * make a backup to tape (always a good idea)
  * backup /boot (no snapshot is posible, non-LVM due to boot requirments)
  * Add a disk to the LVM group (space for the snapshots)
  * extend group to have enough space
  * make a copy of /etc/fstab
  * create snapshots of  / and  /home  to roll back to if needed
  * mount snapshots, and set fstab.rollback version

Update
  * do system updates
  * if successful remove snapshots

Reject the update
  * restore /boot
  * change root= to snapshot root
  * reformat LVM original volume devices
  * Restore /home
      + reformat original /home devive
      + mount as /mnt
      + copy running snapeshot /home to /mnt
      + unmount /mnt
  * Restore / (root)
      + reformat original / device
      + mount as /mnt
      + copy running snapshot / to /mnt
      + validate root restore
  * restore original /etc/fstab
  * Reboot
  * remove LVM snapshot volumes
  * rollback the boot loader

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LVM2

Snapshots can be mounted Read-Write and changed, but remains a snapshot.
Changes are also faster on the snapshot!

Example... Snapshot root, and rename so snapshot is the root!
https://serverfault.com/questions/128878/

  lvrename lvm root root-old
  lvcreate -n root -s lvm/root-old -L 10G

And reboot, and upgrade

You can jump back to old root using...

  lvrename lvm root root-new
  lvrename lvm root-old root
  reboot

As the root-new is the snapshot you can now junk it using...

  lvremove lvm/root-new

Or commit using (on old system)

  lvconvert --merge lvm/root-new

or if you did not jump back...

  lvrename lvm root root-new
  lvconvert --merge lvm/root-new
  lvrename lvm root-old root
  reboot

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