how to use NAS based on fritz.box

[leonundjulie]

I did as required. I mounted to my PI4 with a 120GB SSD (I lost already 2 SD Cards and learned from my mistakes; so I have it on a SSD now) a NAS (Fritz.Box with an attached 120GB SSD, ext4 formated) … I can read, write and delete files on the mounted ssd. So far so good. But starting the RonR and following happens:

Image file to create? /mnt/nasbckp/nasbackup/test.img

Initial image file ROOT filesystem size (MB) [14606]? 15000

Added space for incremental updates after shrinking (MB) [0]? 5000

Create /mnt/nasbckp/nasbackup/test.img (y/n)? y sfdisk: cannot open /mnt/nasbckp/nasbackup/test.img: Das Argument ist ungültig sfdisk: cannot open /mnt/nasbckp/nasbackup/test.img: Das Argument ist ungültig losetup: /mnt/nasbckp/nasbackup/test.img: Warning: file is smaller than 512 bytes; the loop device may be useless or invisible for system tools.

Unable to create image BOOT filesystem

What is the reason? What is the mistake