Balancing does not help with "no space left" despite there is capacity available.

Thanks for reply.

The NAS contains mainly Virtual Machines and we do not backup them.

I’ve freed space to 72% use

# df -h

Filesystem      Size  Used Avail Use% Mounted on

tmpfs            10M  4.0K   10M   1% /dev

/dev/md0        4.0G  472M  3.3G  13% /

tmpfs           3.9G     0  3.9G   0% /dev/shm

tmpfs           3.9G   13M  3.9G   1% /run

tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup

tmpfs           3.9G     0  3.9G   0% /media

/dev/md127      6.5T  4.1T  1.7T  72% /prod

/dev/md127      6.5T  4.1T  1.7T  72% /home

/dev/md127      6.5T  4.1T  1.7T  72% /apps

/dev/md127      6.5T  4.1T  1.7T  72% /run/nfs4/home

/dev/md127      6.5T  4.1T  1.7T  72% /run/nfs4/prod/VMStorage

/dev/md127      6.5T  4.1T  1.7T  72% /run/nfs4/prod/ISO

Balancing made progress to ~70% and failed again with same error.

I’ve got 80% in use back on /prod partition as a result of balancing run and still no luck with “no space left” resolve.

How can I figure out where 600GB disappeared while balancing?

# btrfs filesystem show

Label: '43f63420:root'  uuid: 701c9fe6-995a-4572-b360-dd7986123e77

        Total devices 1 FS bytes used 447.16MiB

        devid    1 size 4.00GiB used 1.53GiB path /dev/md0

Label: '43f63420:prod'  uuid: 96799cff-1ad8-4deb-a06b-758cacfea9bd

        Total devices 1 FS bytes used 4.04TiB

        devid    1 size 6.49TiB used 5.59TiB path /dev/md127

As I understand free workspace is 900GB. Isn't that sufficient?

Is there a way to check what exactly locks the space and which filter to use?

Is that normal that I have to keep more than 1TB free to keep the NAS operational?

Thank you in advance.