Hi,
I’m new to backing up Qubes, so I just tried the “Backup Qubes” tool in the main menu.
I plugged in an external USB SSD, already partitioned, one partition I named “Qubes_backup”, created one “Connect_usb_backup” default Qube (debian-12 template, PVH), attached the whole external SSD to Connect_usb_backup, and the launched the Backup Qubes tool.
I selected 2 qubes to backup (one pvh and one hvm), selected the Qubes_backup partition as destination, but got straitgh away the error in the title, with no details (no read-only for instance).
I’ve tried a ‘touch filename’ in terminal in the destination folder, I cannot write as ‘user’, I can write with ‘sudo touch filename’.
What should I check to understand what went wrong ?
I investigated a bit further, it seems the partition of the external usb ssd is mounted with root permissions (checked with ls -al).
And the “Qubes Backup” does no seem to have enough rights to write on it, this time I got "dd: failed to open /media/usr/qos_backup/qubes_backup_2025xxx: Permission denied", though it is executed from Dom0.
What can be done with “Qubes Backup” not having enough permissions ?
Make the destination directory owned by user:
$ sudo chown user:user /media/usr/qos_backup
Yes, thx, it allows the Qubes Backup tool to reach the partition of the usb drive 
I’m just a bit disturbed since it is not mentioned in the procedure ?
But it seems I’m in trouble with my usb drive, as the partition is randomly mounted in the dedicated vm (or another), though I can see the tar backup file when plugging the usb drive in a debian machine. The ssd (micron CT2000X8SSD9) perfectly comes up in the usb manager, the dedicated partition (qos_bckp) is displayed as attached to the dedicated qube (connect_usb_ssd_backup), but it does not show up in the file manager or the terminal of the vm (and qvm-block lists correctly the partitions and tells qos_bckp is used by connect_usb_ssd_backup).
Eventually, I mounted the xvdi in the terminal. I could access the backup, tested verifying its integrity, and finally restored (as they were test VMs), so I now have my VMs duplicated … for a while (check and then delete).
Thx