(:titla Use Clonezilla:)
No real problem for the backup, but one can't include a raid partition, even btrfs one.
If the goal is to backup a partition, not a bootable disk, it may be easier to use partclone directly or dd piped through gzip (the empty sectors compress nearly a zero).
Clonezilla insist to restore at the very same place it found the source.
That way one can't restore to an external disk, say to found only one file. It's possible if one know the device the external disk will take, but this is unlikely (/dev/sdXY changes all the time)
The faq say:
just in case:
Say if your image is /home/partimag/YOURIMAGE/, and the image is /home/partimag/YOURIMAGE/sda2.ntfs-ptcl-img.gz.aa, sda2.ntfs-ptcl-img.gz.ab..., and you want to restore the image to a file sda2.img which you can mount later. Before you do it, make sure the disk space is big enough for you to store this image file "sda2.img".
Now you can run:
to see it's gzip, bzip or lzop image. Say it's gzip, then you can run
cd /home/partimag/YOURIMAGE/ cat dir/sda2.ntfs-ptcl-img.gz.* | gzip -d -c | partclone.ntfs -r -C --restore_raw_file -s - -o sda2.img mount -o loop sda2.img /mnt
and all the files are in the dir /mnt/.
Partclone* have to be installed in the distro separately.
This didn't work for me at the moment, so I made several steps:
cat /run/media/jdd/50EB-E874/2019-08-18-12-b.img/sdb4.ext4-ptcl-img.gz.* > sdb4.gz
Then open the gz file with ark and unzip.
partclone.ext4 -s sdb4.img -r --restore_raw_file -o sdb4
gives an sdb4 for loop mount
Works if the image is not too big respective the size of the target disk. It's extremely long...