How to know if it is safe to remove block storage

I have a block storage volume-nyc1-01 of 1TB attached to the droplet and we would like to remove it.

The volume has not been mounted yet (no entry in fstab or mtab) so I guess I can simply delete it from dashboard.

But df -h shows that size of docker volumes are more than 60GB (which is systems SSD).

root@ubuntu-4gb-nyc1-01:~# df -h
Filesystem Size Used Avail Use% Mounted on
udev 2.0G 0 2.0G 0% /dev
tmpfs 396M 41M 355M 11% /run
/dev/vda1 59G 12G 47G 21% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
/dev/dm-1 100G 617M 100G 1% /var/lib/docker/devicemapper/mnt/37bcacd5592623173bb4887cfc87c74d57efab37acaa25506f18a6083c742c10
shm 64M 0 64M 0% /var/lib/docker/containers/37bcacd5592623173bb4887cfc87c74d57efab37acaa25506f18a6083c742c10/shm
--- truncated --
tmpfs 396M 0 396M 0% /run/user/0

I would like to know from where these space come from and if its safe to remove the block storage ?

Any help is appreciated.

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As already covered in the comments, if the block storage volume is not mounted it is safe to remove. About the Docker entries, it looks like Docker is configured to use the Device Mapper storage driver. This uses a concept called thin provisioning for storage which “relies on on-demand allocation of blocks of data versus the traditional method of allocating all the blocks in advance.” That means that while Docker has created a local block device, it is not actually utilizing the full amount of space shown. You can find real usage info by running the docker info command and finding the “Storage Driver” section. It should look something like:

Storage Driver: devicemapper
 Pool Name: docker-thinpool
 Pool Blocksize: 524.3 kB
 Base Device Size: 10.74 GB
 Backing Filesystem: xfs
 Data file:
 Metadata file:
 Data Space Used: 212.3 MB
 Data Space Total: 212.6 GB
 Data Space Available: 212.4 GB
 Metadata Space Used: 286.7 kB
 Metadata Space Total: 1.07 GB
 Metadata Space Available: 1.069 GB
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