System volume root's usage is 84%. This condition should not occur under normal conditions. Contact

Please help....

System volume root's usage is 84%. This condition should not occur under normal conditions. Contact technical support.

I keep getting this error, I have a small ammount of knowledge with linux using putty, it is slowly increasing in size i have thought about resetting but i have to much data on the drives is there a way to remove them reset and then rebuild.

root@Home-Server:/# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev             10M  4.0K   10M   1% /dev
/dev/md0        3.7G  3.1G  420M  89% /
tmpfs          1009M     0 1009M   0% /dev/shm
tmpfs          1009M  620K 1008M   1% /run
tmpfs           505M  1.1M  504M   1% /run/lock
tmpfs          1009M     0 1009M   0% /sys/fs/cgroup
/dev/md127      1.9T  610G  1.3T  33% /data
/dev/md127      1.9T  610G  1.3T  33% /apps
/dev/md127      1.9T  610G  1.3T  33% /home

root@Home-Server:/# du -sh *
0       1
7.3G    apps
6.0M    bin
4.0K    boot

root@Home-Server:/# btrfs fi show /data
Label: '116548d8:data'  uuid: b78d3198-a934-4e9e-8249-3986dc467d7f
        Total devices 1 FS bytes used 606.88GiB
        devid    1 size 1.81TiB used 612.07GiB path /dev/md127

btrfs fi df /data

root@Home-Server:/# btrfs fi df /data
Data, single: total=607.01GiB, used=604.98GiB
System, DUP: total=32.00MiB, used=96.00KiB
Metadata, DUP: total=2.50GiB, used=1.90GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

Apps installed: linux - dash, LogAnaylser, Recoll

Thanks in advance for your help.