The system-data folder was smaller then it take less than 5 minutes to backup (and 3 more to restore).

I was thinking about doing it on the SD at the beginning but as my data partition was about 54Go, I was scared that my 32Go SD card wasn't sufficient (as I already had a lot of things on my SD like all the pictures taken by the camera, they are very big on te Pro5 because of the sensor quality).
And one other thing was that my sdcard wasn't mounted on recovery, I think that the recovery-turbo.img miss a lot of features.

For the phone where the system-data and user-data are correctly mounted on the /data folder in recovery, this script can work well if you remove the line "adb shell mount /dev/block/sda44 /data"

But if you want to do that locally on the SD card, if it is mounted, you can do that on the recovery nearly the same way, don't forget to use tar as it will take care of the symlinks (not to ignore them, it will save them too).

It will be very perfect if that can be integrated to the installer !

Sorry I couldn't resist the pointless joke...

I share here how I did:

Backup :

#!/bin/bash
echo "Backing up your data"
adb reboot recovery
sleep 15
adb shell mount /dev/block/sda44 /data
adb shell mkfifo /backup.pipe 
adb exec-out 'tar -cvp data/system-data 2>/backup.pipe' | dd of=system.tar & adb shell cat /backup.pipe &
adb shell rm /backup.pipe
adb shell mkfifo /backup.pipe 
adb exec-out 'tar -cvp data/user-data 2>/backup.pipe' | dd of=user.tar & adb shell cat /backup.pipe &
adb shell rm /backup.pipe
adb reboot

With this script, you will mount the data partition under the recovery mode, create a pipe to transfer the content of the folder (/data/user-data) through stdout to dd on the local computer in a file named user.tar, then it will do the same for the folder system-data.

Now to restore :

#!/bin/bash
echo "Restoring your data"
adb reboot recovery
sleep 15
adb shell mount /dev/block/sda44 /data
adb shell mkfifo /resto.pipe
adb push user.tar /resto.pipe & adb shell 'cd /; cat /resto.pipe | tar -xv'
adb shell rm /resto.pipe
adb shell mkfifo /resto.pipe
adb push system.tar /resto.pipe & adb shell 'cd /; cat /resto.pipe | tar -xv'
adb reboot

This script will boot the phone into recovery mode, mount the sda44 partition into /data folder, push your backup user.tar through the previously created pipe. On the phone the pipe is catched by cat then sent to tar for decompressing.

Your backup needs to be in the same folder as the script restore because I written it like this.

Credits goes there : https://www.forum-generationmobiles.net/t78912-tutoriel-backup-adb-sauvegarde-compressee-des-donnees-de-android-vers-votre-pc-gnu-linux

I tested it and it's perfectly working, I was able to clone one of my Pro 5 to the other one Pro5.

sda44 partition is mostly for Pro5, not sure that this mount works on other model.
I hope that this could help other people.

The best way is maybe to add this feature to ubports-installer, in order to be able to just backup/restore our phone (and of course re-installing it) only with one tool.

What are you thinking about that ?

I used fastboot to flash the recovery_turbo.img (by the way this issue was closed on github but without details : https://github.com/ubports/ubports-installer/issues/599.

I booted on recovery using adb reboot recovery. I mounted sda44 partition on /data :

adb shell mount /dev/block/sda44 /data

Then I tried adb pull /data/system-data ./

But .... it seems not working when they are symlinks and it fail and stop :

~/Documents/Meizu$ adb pull /data/system-data ./
adb: error: failed to copy '/data/system-data/var/log/installer/media-info' to './system-data/var/log/installer/media-info': remote No such file or directory

After a look at this folder we can see :

~ # ls -l /data/system-data/var/log/installer/media-info 
__bionic_open_tzdata: couldn't find any tzdata when looking for localtime!
__bionic_open_tzdata: couldn't find any tzdata when looking for GMT!
__bionic_open_tzdata: couldn't find any tzdata when looking for posixrules!
lrwxrwxrwx    1 root     root            15 Nov 23 13:26 /data/system-data/var/log/installer/media-info -> /etc/media-info
~ # 

How can I then do my backup please ?

[34249.254000] usb 2-1.3: new high-speed USB device number 117 using ehci-pci
[34249.283824] usb 2-1.3: no configurations
[34249.283831] usb 2-1.3: can't read configurations, error -22
[34249.290021] usb 2-1-port3: unable to enumerate USB device

Even Windows is not recognizing it. I have to burn the old recovey-turbo.img from ubuntu and the it works, Am I the only one to have this issue ?

And with the old recovery my /data folder is empty :

~ # ls
cache                init.rc              service_contexts
charger              proc                 sideload
data                 property_contexts    storage
default.prop         ram0                 sys
dev                  res                  system
etc                  root                 tmp
file_contexts        sbin                 ueventd.goldfish.rc
fstab.goldfish       sdcard               ueventd.m86.rc
fstab.m86            seapp_contexts       ueventd.rc
init                 selinux_version
~ # ls /data
~ # 

The user-data partition doesn't seems to be mounted :

~ # mount
rootfs on / type rootfs (rw)
tmpfs on /dev type tmpfs (rw,nosuid,relatime,mode=755)
devpts on /dev/pts type devpts (rw,relatime,mode=600,ptmxmode=000)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
tmpfs on /tmp type tmpfs (rw,relatime)
/dev/block/platform/15570000.ufs/by-name/cache on /cache type ext4 (rw,nodev,noatime,nodiratime,data=ordered)
~ # 

Doing it file-by-file is not ideal, as you will loose all system settings etc. The drawback of recovery is, you cannot do it while booted into the live system. There might be better solutions in the future.