Btrfs and learning...

Also:

df: /run/user/1000/doc: Operation not permitted
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        7.5G     0  7.5G   0% /dev
tmpfs           7.5G  276M  7.2G   4% /dev/shm
tmpfs           7.5G  9.9M  7.5G   1% /run
tmpfs           7.5G     0  7.5G   0% /sys/fs/cgroup
/dev/sda2       3.7T  784G  2.9T  22% /
/dev/sda2       3.7T  784G  2.9T  22% /.snapshots
/dev/sda2       3.7T  784G  2.9T  22% /tmp
/dev/sda2       3.7T  784G  2.9T  22% /root
/dev/sda2       3.7T  784G  2.9T  22% /boot/grub2/i386-pc
/dev/sda2       3.7T  784G  2.9T  22% /boot/grub2/x86_64-efi
/dev/sda2       3.7T  784G  2.9T  22% /var
/dev/sda2       3.7T  784G  2.9T  22% /opt
/dev/sda2       3.7T  784G  2.9T  22% /home
/dev/sda2       3.7T  784G  2.9T  22% /srv
/dev/sda2       3.7T  784G  2.9T  22% /usr/local
/dev/sda1       500M  328K  500M   1% /boot/efi
tmpfs           1.5G   28K  1.5G   1% /run/user/1000

~> lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0  1.8T  0 disk 
├─sda1   8:1    0  500M  0 part /boot/efi
├─sda2   8:2    0  1.8T  0 part /usr/local
└─sda3   8:3    0    2G  0 part [SWAP]
sdb      8:16   0  1.8T  0 disk 

/dev/sda1: SEC_TYPE="msdos" UUID="--------------" TYPE="vfat" PARTUUID="4abc73fb----------------------------------------"
/dev/sda2: UUID="14a57504------------------" UUID_SUB="e385c59d-------------------" TYPE="btrfs" PARTUUID="166090b6---------------------"
/dev/sda3: UUID="32bf01f5-------------------" TYPE="swap" PARTUUID="4128283b-8-------------------"
/dev/sdb: UUID="14a57504-----------------" UUID_SUB="2a1121fe-1a81-----------------------" TYPE="btrfs"