Would like some assistance

[Snowhog]

That's much more helpful (to me). Thank you.

First Issue:

mount /dev/sdb /backup

/backup didn't exist, so I created it on /dev/sda1

Second Issue:

When I plug in my external HDD, the Disk & Devices pop-up notifier appears. I just close the pop-up; I don't click on Mount and Open. In the konsole I type:

mount /dev/sdb /backup

and am told:

mount: /backup: wrong fs type, bad option, bad superblock on /dev/sdb, missing codepage or helper program, or other error.

If I then click on Mount and Open in Disk & Devices, the drive gets mounted and Dolphin opens showing the drive in a separate tab (465.8 GiB Removable Media). If I then repeat the mount command in konsole I get:

mount: /backup: /dev/sdb already mounted or mount point busy.



Update:

After the external HDD was mounted via Disk & Devices, I opened KDE Partition Manager. I selected /dev/sdb and highlighted /dev/sdb1 and right-clicked and selected Unmount.

Opened Konsole and typed:

sudo -i
mount /dev/sdb1 /backup

That worked.

So your instruction: mount /dev/sdb /backup is wrong? Needs to be /dev/sdb1?

[GreyGeek]

Sure enough ...

sudo -i
cd /

to get to root.

Mount the btrfs root file system (<ROOTFS>) to /mnt

mount /dev/sda1 /mnt

If you do
vdir /mnt
you will see

/mnt/@
/mnt/@home

Here's mine:
/mnt
├── @
└── /mnt/snapshots/
├─── @202202251913
├─── @202202262040
├─── @202202281609
├─── @202203011815
└─── @202203022213

You don't see a @home subvolume because I moved @home into @ and commented out the stanza in /etc/fstab that mounts it.

Those two subvolumes, @ and @home, are your live, running system, / and /home. You didn't have to stop the system to do this step. You can continue to use the system while /dev/sda1 is mounted to /mnt.


Plug in and mount the External HDD drive

mount /dev/sdb1 /backup

Create a place to store snapshots that won't be visible to users (you) when /mnt is umounted, and because you don't want to clutter up /mnt with snapshots.

mkdir /mnt/snapshots

Create READ-ONLY snapshots for both @ and @home. Only read-only snapshots can be sent to external subvolumes using the btrfs send command. Using any other tool to create a copy on an external drive can corrupt the subvolume.

btrfs su snapshot -r /mnt/@           /mnt/snapshots/@yyyymmddhhmm
btrfs su snapshot -r /mnt/@home  /mnt/snapshots/@homeyyyymmddhhmm

Now, send the newly creates snapshots to the external USB drive.

btrfs send /mnt/snapshots/@yyyymmddhhmm  | btrfs receive /backup
btrfs send /mnt/snapshots/@homeyyyymmddhhmm  | btrfs receive /backup

Depending on the size of @ and @home, each send can take up to 20-30 minutes. After @yyyymmddhhmm and @homeyyyymmddhhmm are on /backup they will constitute the "parent" snapshot for a subsequent incremental backup, which will take only a few seconds for each one.

Note: do not attempt to use mv to send a snapshot to /backup. It won't work. The mv command only works within a subvolume, NOT between subvolumes. If, in the future, you want to restore your system using a snapshot on HDD then reversing the source and destination is how it is done.

I use the history command to recall previous mount commands and then issue !nnnn, where nnnn is the number of the specific history command I want to use. Saves lots of typing. If done manually, the btrfs send command is also among the history listings and can be copy+pasted and then edited for the new date before hitting the return key.

Next lesson when you are ready.

[Snowhog]

Thanks, but that's just way too much voodoo foo for me. Consider that your script is "at the marathon running stage", and I'm not even able to crawl yet.

My internal HDD (/dev/sda) that Kubuntu 22.04 is installed on is formatted btrfs with one partition (/dev/sda1) (UUID=67fab1ac-b53c-4e10-9faf-f9a434156e) and two sub-volumes: subvol=@ and subvol=@home.

My external USB HDD (/dev/sdb) is formatted btrfs with one partition (/dev/sdb1) (UUID=7baf740a-eab6-40ce-9225-a99a1d0ee969) and no sub-volumes.

K(eep) I(t) S(imple) S(tupid) for me.

All I really want at this point are extremely simple, step-by-step instructions that will create a snapshot of @ that includes @home, and sends it to the external USB.

[GreyGeek]

Here is the result of my backup this evening.

$ sudo -i
root@jerry-hp17cn1xxx:~# cd /
root@jerry-hp17cn1xxx:/# /make_snapshot.sh
Mounting drives
mount: /mnt: /dev/sda3 already mounted on /.
Making today's snapshot
Create a readonly snapshot of '/mnt/@' in '/mnt/snapshots/@202203022213'
Finding previous snapshot as parent
Attempting incremental backup
btrfs send -p /mnt/snapshots/@202203011815 /mnt/snapshots/@202203022213 | btrfs receive /backup
At subvol /mnt/snapshots/@202203022213
At snapshot @202203022213
Delete subvolume (commit): '/mnt/snapshots/@202202242057'
Delete subvolume (commit): '/backup/@202202171957'
Snapshots completed, oldest snapshots deleted
Drives unmounted and 3 syncs done
root@jerry-hp17cn1xxx:/#

[GreyGeek]

Here is the script that I use when I don't do it manually.

#!/bin/bash
#
# script to create backup snapshots to /mnt/snapshots and a differential backup to /backup
# To be run as root from /
#
echo "Mounting drives"
eval "mount /dev/disk/by-uuid/038bd596-59b4-4bb0-98e5-3cbeec1dd339 /mnt"
eval "mount /dev/disk/by-uuid/c16e0247-d866-47f3-8d5e-770e746cd51c /backup"

NOW=$(date +%Y%m%d%H%M)
echo "Making today's snapshot"
MKSNAP='btrfs su snapshot -r /mnt/@ /mnt/snapshots/@'$NOW
eval $MKSNAP
eval 'sync'
eval 'sync'

echo "Finding previous snapshot as parent "
PREVSNAP=""
list=($(ls /mnt/snapshots/))
PREVSNAP=${list[-2]}
NOW=${list[-1]}
echo "Attempting incremental backup"
if [[ -s "/mnt/snapshots/"$PREVSNAP ]];
then
  MKINC='btrfs send -p /mnt/snapshots/'$PREVSNAP
  MKINC=$MKINC' /mnt/snapshots/'$NOW
  MKINC=$MKINC' | btrfs receive /backup'
  echo $MKINC
  eval $MKINC
  eval 'sync'
  eval 'sync'
  eval "sync"
  DELSNAP='btrfs subvol delete -C /mnt/snapshots/'${list[0]}
  eval $DELSNAP
  eval 'sync'
  eval 'sync'
  eval 'sync'
  list=''
  list=($(ls /backup))
  DELSNAP='btrfs subvol delete -C /backup/'${list[0]}
  eval $DELSNAP
  eval 'sync'
  eval 'sync'
  eval 'sync'
  echo "Snapshots completed, oldest snapshots deleted"
  eval 'umount /backup'
  eval 'umount /mnt'
  eval 'sync'
  eval 'sleep 1'
  eval 'sync'
  eval 'sleep 1'
  eval 'sync'
  eval 'sleep 1'
  echo "Drives unmounted and 3 syncs done"
else
  echo 'Incremental backup failed using '$PREVSNAP' and '$NOW
  echo 'Drives still mounted, ready to clean up'
fi

The "PREVSNAP" has to exist on the rootfs subvolume and on the backup subvolume.

Here is what one of my incremental snapshots looked like:
btrfs send -p /mnt/snapshots/@202202262040 /mnt/snapshots/@202202281609 | btrfs receive /backup

The @202202262040, taken on Feb 26, 2022 at 8:40PM, resided on both /mnt/snapshots and /backup. It was sent to the /backup drive by my previous incremental send command. It is the parent snapshot. The snapshot taken on Feb 28, 2022 at 4:09PM is the child snapshot. The receive portion of the incremental command will see the name of the parent snapshot and look for it on the subvolume /backup. Using it as a template, the send portion of the command sends ONLY THE DIFFERENCE between the parent and child snapshots to the receive command. The receive command takes those differences and builds the child snapshot on /backup.

My external 500Gb spinner is plugged in before I run the script. I do not mount it. The script does that. It mounts the external drive to /backup, creates the child snapshot (which becomes the latest snapshot) and then using the previous snapshot, as determined by the list command, the incremental snapshot is taken.

I also have an internal NVMe 1Tb SSD which I mount manually on occasions to make incremental snapshots that may be 3 or more days between the parent and child. Even so, the incremental snapshot rarely takes more than 15 to 20 seconds to complete. Usually less than 10 secs.

Note that in order to use the send command the parent and child snapshots must be "read only", that is, made using the -r switch. My /mnt/snapshot contains:

:~# !1996
mount /dev/sda3 /mnt
root@jerry-hp17cn1xxx:~# vdir /mnt/snapshots/
total 0
drwxr-xr-x 1 root root 334 Feb 10 16:28 @202202242057
drwxr-xr-x 1 root root 334 Feb 10 16:28 @202202251913
drwxr-xr-x 1 root root 334 Feb 10 16:28 @202202262040
drwxr-xr-x 1 root root 334 Feb 10 16:28 @202202281609
drwxr-xr-x 1 root root 334 Feb 10 16:28 @202203011815
root@jerry-hp17cn1xxx:~#

My usage shows:

:~# btrfs filesystem usage /mnt
Overall:
   Device size:                 441.04GiB
   Device allocated:            160.05GiB
   Device unallocated:          280.99GiB
   Device missing:                  0.00B
   Used:                        133.96GiB
   Free (estimated):            305.43GiB      (min: 305.43GiB)
   Data ratio:                       1.00
   Metadata ratio:                   1.00
   Global reserve:              218.44MiB      (used: 0.00B)

Data,single: Size:157.01GiB, Used:132.56GiB (84.43%)
  /dev/sda3     157.01GiB

Metadata,single: Size:3.01GiB, Used:1.39GiB (46.30%)
  /dev/sda3       3.01GiB

And it shows, with my entire system and 5 snapshots, 280.99Gib unallocated. Those same 5 snapshots would fill up my 500Gb spinner and the sixth one would fail to complete because it would run out of space. I learned that by experience.

PS- The UUID's I got by using "blkid" with the external HDD plugged in.

[Snowhog]

For me, understanding btrfs is voodoo magic. I just have a difficult time wrapping my head around it. That said, I have my laptop formatted with btrfs. I also have an external 500 GB HDD, also formatted with btrfs that has nothing on it.

I'd like to play with btrfs full and incremental backups, and that's where I'd like some assistance. If one of you btrfs witch doctors would be so kind as to write two scripts (or two .bash_aliases file entries) that would let me manually do full backups and incremental backups, I'd be indebted. I don't want anything complicated. KISS. The laptop isn't a production unit, and it doesn't have anything important on it.

If one of you is game, let me know what you need to know about my laptop and the external HDD.